The impact of shift length on the operational effectiveness of UK Authorised Firearms Officers: a field experimental study

The impact of shift length on the operational effectiveness of UK Authorised Firearms Officers: a field experimental study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article The impact of shift length on the operational effectiveness of UK Authorised Firearms Officers: a field experimental study Chloe Brennan, Sarah Gordts, Jon Cole This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7272614/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The Police Federation do not recommend 12-hour shifts yet the impact of shift length on cognition, sleepiness, fatigue, and operational effectiveness is largely unknown. A study on the effects of a 12-hour operational shift on armed police officers was conducted with three UK Police Forces. A total of 62 officers were tested from a variety of roles (armed response vehicle crew, specialist firearms officer, and counter terrorism specialist firearms officer). Psychological measures tested levels of fatigue, sleepiness, and working memory, and a training scenario measured operational effectiveness including appropriate use of force at the beginning and end of a shift. Participants showed a significant increase in fatigue, sleepiness, and cognitive performance at the end of the shift. There was no effect on training scenario performance, suggesting that a 12-hour shift does not have an effect on the ability of armed police officers to respond appropriately to a potential armed confrontation. Armed policing Shift length Lethal force Working memory Fatigue 1. Introduction Policing in England and Wales remains a largely unarmed service, and only a proportion of police officers volunteer and are trained as authorised firearms officers (AFOs). In the year ending March 2024, there were only 6,473 operationally deployable armed officers out of 149,164 police officers in the United Kingdom (UK), which represents 3.9% of the total number of police officers (Home Office, 2024 ). The nature of UK armed policing means that AFOs are often only deployed as a last resort, and only to incidents which pose a serious threat (College of Policing, 2013 ). In serious incidents that may require the discharge of a weapon, AFOs must make rapid decisions, where failure to shoot a suspect may endanger themselves and the public. An incorrect decision to shoot will likely result in widespread media attention, a full inquiry, and possibly a court case. Despite the high stakes nature of use of force decisions, there is very little evidence on the impact of shift length on the ability to make appropriate decisions to shoot. A 2019 inquiry into the death of Anthony Grainger, an unarmed man that was shot during a pre-planned operation by Greater Manchester police officers, recommended that the National Police Chiefs’ Council (NPCC) and the College of Policing should decide whether there should be a maximum period during which AFOs are permitted to remain on continuous duty (Home Office, 2019 ). Some of the AFOs participating in the deployment had been on duty for more than 14 hours. Shift patterns within UK policing vary, and those in frontline roles routinely work the shift pattern followed by their police force. Whilst the Police Federation states that shift length should ideally be between 8–10 hours, and do not recommend 12 hour shifts due to health and safety concerns, the impact of shift length on cognitive performance, sleepiness and fatigue, and operational effectiveness is largely unknown. The need for armed police officers to rapidly make life-and death decisions on the appropriate level of force to use in a dangerous situation can be cognitively demanding. Prolonged shift lengths may have a detrimental impact on cognitive performance, though research regarding the impact of shift length on cognitive performance is mixed. Much of this research been carried out in non-policing contexts, and several studies have found lower cognitive performance on tasks such as missing signals on a reaction time task, more frequent errors on a grammatical reasoning task and poorer motor abilities when comparing a 12-hour, 2–4 day schedule as opposed to an 8-hour 5–7 day shift schedule in male control room operators (Rosa & Bonnet, 1993 ; Rosa & Colligan, 1992 ). Whilst these studies are relatively outdated, a recent systematic review by Leso et al., ( 2021 ) showed that across workplaces, cognitive performance can progressively worsen over consecutive night shifts, or exposure to very long work shifts, as defined as working 41 or more hours per week. For instance, among petrochemical control room shift workers, cognitive performance on a continuous performance test, n-back test, and simple reaction time test was significantly worse at the end of a 12-hour shift (Kazemi et al., 2016 ). However, even the picture here is not clear cut, as research shows that whilst working long shifts can cause some cognitive functions to deteriorate, others do not, or even improve (Tadinac et al., 2014 ). Generally, working a very extended shift can cause deterioration in cognitive function, as demonstrated by medical interns having higher rates of attentional failures when working a 30-hour compared to 16-hour shift (Lockley et a., 2004). However, when comparing cognitive efficiency on a measure of working memory, anaesthesiology residents showed a significant improvement after, compared to before working a 24-hour shift, and concentration did not diminish (Lockley et al., 2004 ). Therefore, some cognitive functions may improve or remain unaffected. This supports a review of several studies which found no differences in critical thinking skills among nurses (Bernreuter et al., 1995), and a study that compared 8-hour vs 10-hour shifts of air traffic control specialists and found no differences in cognitive performance and alertness on tasks such as reaction time or digit addition (Schroeder et al., 1998 ). There has been much less research in a policing context, though a study of 200 police officers in the United States (US) found no significant differences in alertness and vigilance when comparing 8-hour, 10-hour, and 12-hour shifts (Amendola et al., 2011 ). This study compared different shift lengths, as opposed to comparing cognitive performance before and after a 12-hour shift, so more research is required on the impact of a 12-hour shift on cognitive performance in officers. A second important factor that may be impacted by extended shift lengths is fatigue, though the research on fatigue, sleepiness, and alertness is also mixed. Vila et al., ( 2000 ) suggested fatigue could increase fearfulness, irritability, and lead officers to make inappropriate decisions or engage in misconduct, and found fatigue can have a negative impact on worker health, safety, and performance (Vila, 2006 ). Canadian police officers found higher levels of self-reported fatigue in officers on 12-hour shifts as opposed to 9-hour shifts (DeCarufel & Schaan, 1990 ) and research with US police officers found that 12-hour shifts are associated with greater sleepiness and less alertness than an 8- and 10-hour shift (Amendola et al., 2011 ). Furthermore, other studies have reported a significant decrease in stress and fatigue in officers following a switch to a 12-hour shift (Pierce & Dunham, 1992 ) or reported no difference between 8- to 12-hour shifts (Smith et al., 1998 ). Most importantly, whilst there may be an increase in feelings of fatigue on longer shifts, this does not transfer to objective measures of fatigue (Smith et al., 1998 ), nor reductions in operational effectiveness (Amendola et al., 2011 ; Sundermeier, 2008 ). Operational effectiveness of armed police officers is arguably the most important factor to consider in the context of shift length. Sundermeier ( 2008 ) reported no reductions in performance in a Midwestern law enforcement agency, and Amendola et al., ( 2011 ) found no differences between 8, 10 and 12-hour shifts in interpersonal interactions, shooting skills, and risky driving behaviours in a sample of over 200 US police officers. In fact, other factors may be more relevant. Blake and Cumella ( 2015 ) found poor sleep quality, greater total time awake, more days worked, and working night or swing shifts as opposed to day shifts decreased the accuracy of police officers’ decision making, particularly for ambiguous scenarios requiring inhibitory control (‘no shoot scenarios’). The policing literature overwhelmingly relates to studies of armed US patrol officers that failed to find any effects on the use of force (although this was rarely measured directly). Given the differences between UK and US policing it is questionable whether this research evidence is directly applicable in the UK. However, the extremely low number of weapon discharges relative to the number of AFO deployments suggests that normal working practices do not routinely lead to the discharge of weapons. In the year ending March 2024, out of 7,589 firearms operations, there were only two incidents in which police firearms were intentionally discharged (Home Office, 2024 ). The current study was therefore undertaken to identify whether a 12-hour shift affected the operational performance of armed police officers in the UK. Operational performance included measures of working memory, fatigue, sleepiness, and use of force decision-making. The hypotheses tested were that police officers would be affected by working a 12-hour shift. Specifically, it was hypothesised that self-reported fatigue and sleepiness would increase, and working memory capacity would decrease, after a 12-hour shift compared to before. It was also hypothesised that operational performance would not significantly differ after compared to before a 12-hour shift. 2. Materials and Method 2.1. Design A within-subjects design was used to compare the operational performance of armed police officers immediately before, and immediately after an operational 12-hour shift. 2.2. Participants A sample of operational firearms officers were recruited via convenience sampling from three police forces across the United Kingdom. A sample size calculation in GPower 3.1 (Faul et al., 2009 ) indicated that a minimum sample size of n = 34 should be recruited to detect moderately sized differences, with a significance level set at α = .05 and power set at β = .80. The final sample consisted of 62 serving police officers which included 42 Armed Response Vehicle (ARV) officers, 19 Counter Terrorism Specialist Firearms Officers (CTSFO) and one Specialist Firearms Officer (SFO). 2.3. Measures Samn-Perelli Fatigue Scale ( SPS; Samn & Perelli, 1982 ). This scale is a commonly used measure of subjective fatigue. Participants are asked to respond to a single item asking how fatigued they feel using a scale ranging from 1 (fully alert, wide awake, ‘extremely peppy’) to 7 (completely exhausted, unable to function effectively, ‘ready to drop’). Karolinska Sleepiness Scale (KSS; Akerstedt & Gillberg, 1990 ). The KSS is a commonly used measure of situational sleepiness. Participants are asked to respond to a single item probing their current levels of sleepiness and alertness. The scale requires participants to rate their levels of sleepiness on a scale ranging from 1 (extremely alert) to 9 (very sleepy, great effort to feel alert, fighting sleep). Operational performance. Four scenarios were specifically developed by police firearms trainers in line with standard practice in UK firearms training. In each scenario, participants were individually briefed to respond to a situation where the police use of firearms might occur. In two scenarios, the appropriate and proportional use of force outcome was to not use force (i.e., ‘no shoot’), and in two scenarios the appropriate and proportional use of force outcome was to use force (i.e., ‘shoot’). Two firearms instructors observed the scenario, and one firearms instructor acted as the role player (i.e., a member of the public). All three instructors scored the scenario as a group immediately after the scenario had concluded. To score the scenario, a five-item scale was developed by the police training facilities. Instructors indicated on a 3-point scale (1 = performed below expectations, 2 = performed as expected, 3 = performance exceeded expectations) how the participant scored on: (1) officer presence, (2) tactical movement; (3) Naturalistic Decision-Making (NDM) Assessment (escalation or de-escalation of potential use of force) (4) communication/negotiation and (5) outcome ( appropriate use of force at the relevant time; see Table 1 below). Scores on all five scenario components were summed to create a total score for overall scenario performance, with higher scores reflecting better performance. It is important to note that for the NDM Assessment and outcome criterion, higher scores do not correspond to higher force but rather to an appropriate management of force depending on the nature of the scenario (i.e., shoot or no-shoot). Table 1 Scoring criteria and their descriptions for the scenarios. Officer Presence Did the officer identify themselves as an Armed Police Officer? Did they attempt to make face to face communication as soon as practicable? Tactical Movement Did the officer make best use of effective cover, move position to maintain communication without placing themselves in danger? Did officers contain the subject? ‘Blue on Blue’. NDM Assessment (Escalation/de-escalation of potential use of force) Did the officer respond to the communications and body movement appropriately (i.e. weapon position aim/off -aim/ready/south/not drawn)? Use of force (consider less lethal options). Communication/Negotiation Did the officer communicate/negotiate at the appropriate level (i.e. Tone/volume/not repetitive/ clear and easily understood)? Outcome Did the officer use the appropriate force at the relevant time (i.e., shoot in the shoot scenario, and do not shoot in the no-shoot scenario)? Automated Operation Span Task (OSpan; Conway et al., 2005 ). The OSpan was used as a measure of working memory capacity. In this task, participants are presented with a series of math problems (e.g., “8 * 3 + 2 = 32) which are followed by a letter sequence (e.g., “TLQ”). Participants are asked to decide whether the answer to the math problem is correct, and then recall the exact letter sequence using a letter matrix. The task consists of a practice session (22 trials) and a test session (15 trials). The practice session involves recalling short letter sequences, practicing the math task, and practicing combining the math problems with the letter sequence recall. The test session consists of 15 trials where each presents a math problem and a letter sequence made up of 3, 4, 5, 6, or 7 letters. The OSpan generates a total score for the ‘operation span’ for each participant, which is the total number of letter sequences that participants could accurately remember in the test session. For example, if a participant correctly recalled 3 letters in a set size of 3, and 4 letters in a set size of 4, and 5 letters in a set size of 6, their operation span would be 3 + 4 + 0 = 7. 2.4. Procedure In the first hour of a 12-hour shift, five participants entered a classroom and were given a participant ID code. Following an explanation of the study and information sheet, participants provided written informed consent, and responded to paper copies the sleepiness and fatigue scales. Next, participants completed the OSpan task via Inquisit software (Inquisit 5, 2016) on a Microsoft tablet. After completion of the task, participants individually took part in scenarios which were held in a firing range in the same building. There were four possible scenarios, which were counterbalanced. Each participant was briefed by the firearms instructor on the scenario and then entered the firearms range. In the range, there were two instructors observing the scenario, and one ‘stooge’ instructor acting as a member of the public. On completion of the scenario, the participant was thanked and then asked to leave, and the three instructors scored the scenarios. Participants returned to repeat the testing procedure in the final hour of their shift. Scenarios were counterbalanced so participants would not take part in the same scenario at the start and end of their shift. 2.5. Data analysis Scores for the fatigue and sleepiness scales, scenario performance and operation span task before and after a 12-hour shift were compared for all participants using parametric tests (i.e., paired sample t-test) for normally distributed and continuous data and non-parametric tests (i.e., Wilcoxon signed rank test) for non-normally distributed and/or ordinal-level data. Cohen’s d was used as the effect size for paired sample t-tests, r was calculated to estimate the effect size for Wilcoxon signed rank test. Because multiple comparisons were conducted, a Bonferroni correction was applied to correct for Type I errors (i.e., detecting a significant difference when there is none) which reduced the significance level to α = .013. 3. Results Self-reported fatigue Participants felt significantly more fatigued at the end of the shift compared to the start of the shift, W = 745.00, Z = 3.44, p < .001, r = .44, and this difference was moderate in size. See table 2 for descriptive statistics. Self-reported sleepiness Participants reported higher levels of sleepiness at the end of the shift compared to the start of the shift, W = 731.50, Z = 2.47, p = .013, r = .31. This difference was moderate in size but only marginally significant. Scenario performance There was no significant difference in overall scenario performance between the end of the shift and the start of the shift, W = 478.00, Z = - 0.45, p = .651, r = .06 Working memory (operation span) [1] Participants had a greater operation span at the end of the shift compared to the start of the shift , t (60) = -3.51, p < .001, d = 0.45, and this difference was small in size. Table 2. Descriptive statistics for fatigue, sleepiness, scenario performance and operation span before and after the 12-hour shift. At the start of the shift At the end of the shift Fatigue 3.00 (5.00) 4.00 (5.00) Sleepiness 3.00(7.00) 4.00(7.00) Operation span 38.21(16.06) 44.90(16.40) Scenario performance 10.00(10.00) 11.00(7.00) Note: Scores are measured on a scale ranging from 1 - 7 (fatigue), 1 - 9 (sleepiness), 0 - 75 (Operation span), and 5 - 15 (Scenario performance). Values for operation span are mean and standard deviation (±SD). Values for fatigue, sleepiness, and scenario performance are median and range. [1] One participant indicated they did not understand the task and their corresponding data was subsequently coded as missing for this analysis. 4. Discussion This is the first study to measure the impact of shift length on the operational performance of AFOs in the UK. Results showed that there was a significant increase in self-reported fatigue and a marginally significant increase in sleepiness at the end of an operational 12-hour shift. There was a potentially paradoxical significant increase in working memory capacity at the end of the 12-hour shift. The training scenario performance, which was used to measure operational effectiveness including appropriate use of force, was not significantly affected by a 12-hour operational shift despite the increased self-reported fatigue and sleepiness. The results therefore suggest that police officers are able to respond appropriately to a (potential) armed confrontation at the end of a 12-hour shift despite self-reporting greater levels of fatigue and sleepiness. The ‘common sense’ view is that a 12-hour shift should affect AFO performance, however the available literature often does not support that opinion. Armed police officers in this study were, however, more fatigued and sleepier at the end of a 12-hour shift, which is generally supported in the literature. Amendola et al., ( 2011 ) similarly found higher levels of sleepiness and alertness in US police officers that worked 12-hour, as opposed to 10-hour or 8-hour shifts, and deCarufel and Schaan ( 1990 ) reported similar findings in Canadian police officers when comparing 12-hour and 9-hour shifts. Some research has found no differences (Smith et al., 1998 ), or even a reduction in fatigue in officers following a switch to a 12-hour shift (Pierce & Dunham, 1992 ) which does not align to our findings. This may be explained by individuals on shorter shifts getting less sleep and having poorer sleep quality, and total time awake has been linked with a reduction in police officer decision making (Blake & Cumella, 2015 ). It is also important to consider the preferences of police officers when introducing any changes to shift length policy, for example, despite officers in deCarufel and Schaan’s ( 1990 ) study reporting greater fatigue, they did not wish to return to an 8-hour shift given their preference for a 12-hour shift schedule. Furthermore, whilst armed police officers in the current study were more fatigued and sleepy, this did not transfer to objective measures of performance in line with previous research (Amendola et al., 2011 ; Sundermeier, 2008 ). The operational effectiveness of armed police officers in the current study, as measured by the training scenario performance, was not affected by a 12-hour operational shift. These scenarios tested the appropriate and proportional use of force (if necessary) using scripted live role plays and were designed to test whether the participants were able to function effectively in their role. This meant that in two scenarios the participants were required to discharge their weapon systems to neutralise the threat posed by the role player and in two they were not. The results therefore suggest that police officers are able to respond appropriately to a (potential) armed confrontation at the end of a 12-hour shift despite self-reporting greater levels of fatigue and sleepiness. This supports research by Amendola et al., ( 2011 ) that found no differences between 8, 10 and 12-hour shifts in interpersonal interactions, shooting skills, and risky driving behaviours in a sample of over 200 US police officers, and by Sundermeier ( 2008 ) that reported no reductions in performance in a Midwestern law enforcement agency. Given that the policing literature overwhelmingly relates to studies of armed US patrol officers, and there are significant differences between UK and US policing, there is a need to understand whether these findings translate to UK policing. Whilst all police officers in the US carry firearms while on duty, in the UK only 3.9% of the total number of police officers are armed (Home Office, 2024 ). The current findings demonstrate that the failure to find effects on the use of force in US officers does generalise to UK armed police officers. This aligns to real use of force decisions which shows in 2024, out of 7,589 firearms operations, there were only two incidents in which police firearms were intentionally discharged (Home Office, 2024 ). Thus, normal working practices do not seem to routinely lead to the discharge of weapons. The findings of this study suggest that whilst there was an increase in fatigue and sleepiness, paradoxically there was also a small increase in cognitive performance. Working memory was measured using the OSpan, which is designed to measure the capacity to maintain and manipulate information in working memory while performing other tasks (Conway et al., 2005 ). The literature is mixed with regards to the impact of shift length on cognitive performance. Whilst some studies indicate lower cognitive performance during 12-hour vs 8-hour shifts in non-policing industries (Rosa & Bonnet, 1993 ; Rosa & Colligan, 1992 ), or at the end as opposed to the start of a 12-hour shift (Kazemi et al., 2016 ), other research found no differences (Bernreuter, & Sullivan, 1995 ; Schroeder, Rosa, & Witt, 1998 ). Amenadola et al., (2011) also found no differences in the cognitive performance of police officers in the US between different shift lengths. However, these studies did not find a positive increase in cognitive performance. Whilst the findings of the current study, that working memory capacity increased may seem unexpected, the literature suggests that the link between shift length and cognitive may be more nuanced. Anaesthesiology residents showed a significant improvement in working memory after, compared to before working a 24-hour shift, and concentration did not diminish (Tadinac et al., 2014 ). Therefore, some cognitive functions may improve or remain unaffected, which may explain the increase in working memory in our study. A second explanation could be that the increase in cognitive performance is due to practice effects. A study by Taylor et al., ( 2019 ) found practice effects for several working memory tests in a study on the impact of fatigue on cognitive performance in UK police officers during a forward rotating shift pattern. Similar learning effects have been observed in non-policing samples in relation to working memory and mental fatigue (Pergher et al., 2021 ). Future research is required to better tease apart the reasons for an increase in cognitive performance in this study. These findings have potential policy implications. In the aftermath of the Anthony Grainger Inquiry (Home Office, 2019 ), the NPCC and College of Policing were tasked with deciding whether there should be a maximum period during which AFOs are permitted to remain on continuous duty. Furthermore, the Police Federation states that shift length should ideally be between 8–10 hours, and do not recommend 12 hour shifts due to health and safety concerns. The findings of this experiment contradict this recommendation and indicate that whilst there may be an increase in fatigue and sleepiness, there is also potentially a small increase in cognitive performance, and no impact on the operational effectiveness of armed police officers. Our findings suggest that armed police officers are not more likely to discharge their weapon inappropriately at the end of a 12-hour shift. Furthermore, it is important to take police officers shift preferences into account when making policy changes, as deCarufel & Schaan ( 1990 ) found officers preferred a 12-hour shift compared to 8-hour shift length. Furthermore, whilst not significant, officers working 12-hour shifts reported higher levels of sleep and worked less overtime than those on 8-hour shifts (Amendola et al., 2011 ). Future research could be conducted to understand officers’ preferences different shift lengths, and how these impact their perceived levels of stress, and account for the impact on overall sleep levels. Blake and Cumella ( 2015 ) found police officers with poor sleep quality and greater total time awake made more inaccurate use of force decisions, particularly when presented with no-shoot and ambiguous scenarios, so the recommendation that police work 8-hour shifts may be counter-intuitive. It is possible that there is a sweet spot, as Amendola et al., ( 2011 ) found a 10-hour shift was the most effective shift length, though future research with UK armed police officers would need to investigate this further. Our study has several strengths and limitations. The study is novel, providing the first preliminary evidence that the operational performance of AFOs in the UK is not significantly negatively impacted by a 12-hour shift. Armed police officers in the current study were tested immediately before, and after an operational shift, and responded to a live fire exercise, where two instructors observed the scenario, and one ‘stooge’ instructor acted as a member of the public. The armed police officers in the experiment needed to decide on the appropriate use of force (i.e., a shoot or no-shoot) depending on the nature of the scenario, using blank firing weapons. In contrast to previous research in this area, that either used computer-based decisions on the use of force (Blake & Cumella, 2015 ) or required police officers to respond to a video-based simulator (Amendola et al., 2011 ), the current study is more ecologically valid. However, it is important to note that this study, like every other study of this nature, has some limitations that need to be considered. The sample size was not large enough to detect small effects, and the non-significant differences in operational performance may be attributable to the use of non-parametric tests, which typically reduce the likelihood of detecting significant differences. However, given that the results of this study suggest a non-significant increase in operational performance after the shift, the inability to detect small effects does not indicate that operational performance would decrease post-shift. It is however possible that a 12-hour shift could cause problems for individual participants because of what happens on that shift, and individual and situational factors could influence decision-making in high stake environments. Therefore, it is not possible to emphatically state that shift length will not cause a performance decrement for every armed officer in the UK on every shift. Even though undetected differences may be small in statistical terms, they could have a potentially detrimental impact considering the context. In addition to this, to keep with the applied nature of the study, standard scoring procedures were used that were developed by training officers for this type of training exercise. The range of scores for the scenario outcome was small, partly due to the rating scale used. A more refined scoring procedure would have allowed for more advanced statistical analysis and may have identified fine grained effects in terms of operational performance, but the unfamiliarity of the training staff in using that scoring system may have caused more problems than it solved. In the absence of a universally agreed method of scoring scenarios of this type it is not possible to determine the impact of the system used on the results obtained. Furthermore, the current study tested AFO performance in training scenarios. Although the scenarios were designed by experienced firearms trainers and are highly similar to the scenarios used in AFO training, it is possible that AFO performance in real (potential) armed confrontations is impacted differently compared to AFO performance in training scenarios. Lastly, the study design did not allow comparing performance between ‘shoot’ and ‘no-shoot’ scenarios. The current findings therefore cannot indicate whether shift length specifically affects decision-making in situations that require inhibitory control, which are precisely scenarios that could lead to inappropriate use of (potentially lethal) force. While the current results suggest that operational performance is not affected, future research should disentangle the effect of shift length on different scenario types. Given that Blake and Cumella ( 2015 ) found police officers with poorer sleep quality, greater total time awake, more days worked, and working night or swing shifts had less accurate decision-making particularly in no-shoot scenarios, future research teasing apart the impact of a 12-hour shift length on scenario type would be beneficial. 5. Conclusion The results of this study suggest that a 12-hour shift increases self-reported fatigue and sleepiness but does not affect the actual performance of armed police officers. There was no evidence that (potentially lethal) force was used more inappropriately after, as opposed to before a 12-hour shift. Potential smaller effects of 12-hour shifts on AFO performance could be tested in future with larger samples. Declarations Acknowledgements: We also sincerely appreciate the support of the three police forces for facilitating the study Ethical Approval This study received ethical approval from the University of Liverpool's Research Ethics Committee (Approval No: 8638). All research activities were conducted in full compliance with the University’s Ethical Review Policy and in accordance with the principles of the Declaration of Helsinki. Prior to participation, all participants provided written informed consent after receiving comprehensive information about the study’s aims, procedures, confidentiality safeguards, voluntary nature of participation, and their right to withdraw at any time without penalty. Funding This work was supported by the National Police Chief’s Council. Availability of data and materials Data are available upon reasonable request. Data from this study will be made available upon reasonable request by contacting the corresponding author at [email protected] . Data will be made available for 10 years in line with ethical considerations. References Amendola, K. L., Weisburd, D., Hamilton, E. E., Jones, G., & Slipka, M. (2011). An experimental study of compressed work schedules in policing: Advantages and disadvantages of various shift lengths. Journal of Experimental Criminology, 7 , 407–442. https://www.policinginstitute.org/wp-content/uploads/2015/06/Amendola-et-al.-2011-The-Impact-of-Shift-Length-Full-Report-.pdf Akerstedt, T., & Gillberg, M. (1990). Subjective and objective sleepiness in the active individual. International Journal of Neuroscience, 52 , 29–37. https://doi.org/10.3109/00207459008994241 Bernreuter, M., & Sullivan, M. (1995). Survey and critique of studies related to shift length variations in nursing from 1970 to 1993. International Journal of Nursing Studies, 32 (2), 188–197. https://doi.org/10.1016/0020-7489(94)00026-G Blake, D., & Cumella, E. (2015). Factoring fatigue into police deadly force encounters: Decision-making and reaction times. Law Enforcement Executive Forum, 15 (1), 44–65. College of Policing. (2013). Armed policing . https://www.college.police.uk/app/armed-policing Conway, A. R. A., Kane, M. J., Bunting, M. F., Hambrick, D. Z., Wilhelm, O., & Engle, R. W. (2005). Working memory span tasks: A methodological review and user’s guide. Psychonomic Bulletin & Review, 12 (5), 769–786. DeCarufel, A., & Schaan, J. L. (1990). The impact of compressed work weeks on police job involvement. Canadian Police College Journal . https://www.ojp.gov/ncjrs/virtual-library/abstracts/impact-compressed-work-weeks-police-job-involvement Faul, F., Erdfelder, E., Buchner, A., & Lang, A. (2009). Statistical power analyses using G*Power 3.1: Tests for correlation and regression analysis. Behavior Research Methods, 41 , 1149–1160. Home Office. (2019). Antony Grainger inquiry: Report into the death of Anthony Grainger . https://www.gov.uk/government/publications/anthony-grainger-inquiry-report-into-the-death-of-anthony-grainger Home Office. (2024). Police use of firearms statistics, England and Wales: April 2023 to March 2024 . https://www.gov.uk/government/statistics/police-use-of-firearms-statistics-april-2023-to-march-2024 Inquisit 5 [Computer software]. (2016). Millisecond Software. https://www.millisecond.com Kazemi, R., Haidarimoghadam, R., Motamedzadeh, M., Golmohamadi, R., Soltanian, A., & Zoghipaydar, M. R. (2016). Effects of shift work on cognitive performance, sleep quality, and sleepiness among petrochemical control room operators. Journal of Circadian Rhythms, 14 (1). https://doi.org/10.5334/jcr.134 Leso, V., Fontana, L., Caturano, A., Vetrani, I., Fedele, M., & Iavicoli, I. (2021). Impact of shift work and long working hours on worker cognitive functions: Current evidence and future research needs. International Journal of Environmental Research and Public Health, 18 (12), 6540. https://doi.org/10.3390/ijerph18126540 Lockley, S. W., Cronin, J. W., Evans, E. E., Cade, B. E., Lee, C. J., Landrigan, C. P., ... & Czeisler, C. A. (2004). Effect of reducing interns' weekly work hours on sleep and attentional failures. New England Journal of Medicine, 351 (18), 1829–1837. https://doi.org/10.1056/NEJMoa041404 Pergher, V., Vanbilsen, N., & Van Hulle, M. (2021). The effect of mental fatigue and gender on working memory performance during repeated practice by young and older adults. Neural Plasticity, 2021 , Article 6612805. https://doi.org/10.1155/2021/6612805 Pierce, J. L., & Dunham, R. B. (1992). The 12-hour work day: A 48-hour, eight-day week. Academy of Management Journal, 35 (5), 1086–1098. Rosa, R. R., & Bonnet, M. H. (1993). Performance and alertness on 8 h and 12 h rotating shifts at a natural gas utility. Ergonomics, 36 (10), 1177–1193. https://doi.org/10.1080/00140139308967987 Rosa, R. R., & Colligan, M. J. (1992). Application of a portable test battery in the assessment of fatigue in laboratory and worksite studies of 12-hour shifts. Scandinavian Journal of Work, Environment & Health , 113–115. http://www.jstor.org/stable/40966090 Samn, S. W., & Perelli, L. P. (1982). Estimating aircrew fatigue: A technique with implications to airlift operations (SAM-TR-82-21). USAF School of Aerospace Medicine. Schroeder, D. J., Rosa, R. R., & Witt, L. A. (1998). Some effects of 8-vs. 10-hour work schedules on the test performance/alertness of air traffic control specialists. International Journal of Industrial Ergonomics, 21 (3–4), 307–321. https://doi.org/10.1016/S0169-8141(97)00044-9 Smith, L., Folkard, S., Tucker, P., & MacDonald, I. (1998). Work shift duration: A review comparing eight hour and 12 hour shift systems. Occupational and Environmental Medicine, 55 (4), 217–229. https://doi.org/10.1136/oem.55.4.217 Sundermeier, J. (2008). A look at the 12-hour shift: The Lincoln police department study. The Police Chief, 75 (3). https://www.ojp.gov/ncjrs/virtual-library/abstracts/look-12-hour-shift-lincoln-police-department-study Tadinac, M., Ante, S., Ivana, H., Branka, M. S., & Romina, I. (2014). Age and individual sleep characteristics affect cognitive performance in anesthesiology residents after a 24-hour shift. Acta Clinica Croatica, 53 (1), 22–30. https://hrcak.srce.hr/126143 Taylor, Y., Merat, N., & Jamson, S. (2019). The effects of fatigue on cognitive performance in police officers and staff during a forward rotating shift pattern. Safety and Health at Work, 10 (1), 67–74. https://doi.org/10.1016/j.shaw.2018.08.003 Vila, B. J., Kenney, D. J., Morrison, G. B., & Reuland, M. (2000). Evaluating the effects of fatigue on police patrol officers: Final report. Police Executive Research Forum . https://www.ojp.gov/pdffiles1/nij/grants/184188.pdf Vila, B. J. (2006). Impact of long work hours on police officers and the communities they serve. American Journal of Industrial Medicine, 49 (11), 972–980. https://doi.org/10.1002/ajim.20333 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7272614","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":507616996,"identity":"49ae5303-984e-4e6d-8f9e-531cb0adb534","order_by":0,"name":"Chloe Brennan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+ElEQVRIiWNgGAWjYDACCSjNz87YAGGxQygDglokm2FamInVYnAYJkJIC//s3oePC3fY5RkfZm6T+Ljnjhw/MwPjhx8Mh41xWnLnuLHxzDPJxWaHGdskZzx7ZizZzMAs2cNw2AyXFgOJNDZp3jbmxG2HGZuNeQ4cTtwAdKE0A8NhGzxa2H/zttUnbm4GavkD0cL8m4AWNmbeNqBKZsbGxwwQLWwgW3A6TOLOMWagw44nzjjM2Piw5wDIL4xtlj0G6Ti9zz+7jfEzb1t1Yn97+4MDPw4AQ4y9+fCNHxXWhg249KCBA0AMilPcEYlVyygYBaNgFIwCVAAAh69Symh8FR4AAAAASUVORK5CYII=","orcid":"","institution":"University of Liverpool","correspondingAuthor":true,"prefix":"","firstName":"Chloe","middleName":"","lastName":"Brennan","suffix":""},{"id":507616999,"identity":"f0282a03-a4d4-49ec-bae1-64039dc82edb","order_by":1,"name":"Sarah Gordts","email":"","orcid":"","institution":"University of Liverpool","correspondingAuthor":false,"prefix":"","firstName":"Sarah","middleName":"","lastName":"Gordts","suffix":""},{"id":507617001,"identity":"6d001d45-2ce7-4641-8e15-7981de814be1","order_by":2,"name":"Jon Cole","email":"","orcid":"","institution":"University of Liverpool","correspondingAuthor":false,"prefix":"","firstName":"Jon","middleName":"","lastName":"Cole","suffix":""}],"badges":[],"createdAt":"2025-08-01 15:23:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7272614/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7272614/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105858921,"identity":"75c6b9ec-f159-4f98-99e1-a8b17e9d72be","added_by":"auto","created_at":"2026-04-01 00:24:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":466528,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7272614/v1/df0a9c8b-c3f6-4c88-817c-75df0e5976c1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The impact of shift length on the operational effectiveness of UK Authorised Firearms Officers: a field experimental study","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003ePolicing in England and Wales remains a largely unarmed service, and only a proportion of police officers volunteer and are trained as authorised firearms officers (AFOs). In the year ending March 2024, there were only 6,473 operationally deployable armed officers out of 149,164 police officers in the United Kingdom (UK), which represents 3.9% of the total number of police officers (Home Office, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The nature of UK armed policing means that AFOs are often only deployed as a last resort, and only to incidents which pose a serious threat (College of Policing, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In serious incidents that may require the discharge of a weapon, AFOs must make rapid decisions, where failure to shoot a suspect may endanger themselves and the public. An incorrect decision to shoot will likely result in widespread media attention, a full inquiry, and possibly a court case. Despite the high stakes nature of use of force decisions, there is very little evidence on the impact of shift length on the ability to make appropriate decisions to shoot. A 2019 inquiry into the death of Anthony Grainger, an unarmed man that was shot during a pre-planned operation by Greater Manchester police officers, recommended that the National Police Chiefs\u0026rsquo; Council (NPCC) and the College of Policing should decide whether there should be a maximum period during which AFOs are permitted to remain on continuous duty (Home Office, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Some of the AFOs participating in the deployment had been on duty for more than 14 hours. Shift patterns within UK policing vary, and those in frontline roles routinely work the shift pattern followed by their police force. Whilst the Police Federation states that shift length should ideally be between 8\u0026ndash;10 hours, and do not recommend 12 hour shifts due to health and safety concerns, the impact of shift length on cognitive performance, sleepiness and fatigue, and operational effectiveness is largely unknown.\u003c/p\u003e\u003cp\u003eThe need for armed police officers to rapidly make life-and death decisions on the appropriate level of force to use in a dangerous situation can be cognitively demanding. Prolonged shift lengths may have a detrimental impact on cognitive performance, though research regarding the impact of shift length on cognitive performance is mixed. Much of this research been carried out in non-policing contexts, and several studies have found lower cognitive performance on tasks such as missing signals on a reaction time task, more frequent errors on a grammatical reasoning task and poorer motor abilities when comparing a 12-hour, 2\u0026ndash;4 day schedule as opposed to an 8-hour 5\u0026ndash;7 day shift schedule in male control room operators (Rosa \u0026amp; Bonnet, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Rosa \u0026amp; Colligan, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). Whilst these studies are relatively outdated, a recent systematic review by Leso et al., (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) showed that across workplaces, cognitive performance can progressively worsen over consecutive night shifts, or exposure to very long work shifts, as defined as working 41 or more hours per week. For instance, among petrochemical control room shift workers, cognitive performance on a continuous performance test, n-back test, and simple reaction time test was significantly worse at the end of a 12-hour shift (Kazemi et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eHowever, even the picture here is not clear cut, as research shows that whilst working long shifts can cause some cognitive functions to deteriorate, others do not, or even improve (Tadinac et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Generally, working a very extended shift can cause deterioration in cognitive function, as demonstrated by medical interns having higher rates of attentional failures when working a 30-hour compared to 16-hour shift (Lockley et a., 2004). However, when comparing cognitive efficiency on a measure of working memory, anaesthesiology residents showed a significant improvement after, compared to before working a 24-hour shift, and concentration did not diminish (Lockley et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Therefore, some cognitive functions may improve or remain unaffected. This supports a review of several studies which found no differences in critical thinking skills among nurses (Bernreuter et al., 1995), and a study that compared 8-hour vs 10-hour shifts of air traffic control specialists and found no differences in cognitive performance and alertness on tasks such as reaction time or digit addition (Schroeder et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). There has been much less research in a policing context, though a study of 200 police officers in the United States (US) found no significant differences in alertness and vigilance when comparing 8-hour, 10-hour, and 12-hour shifts (Amendola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This study compared different shift lengths, as opposed to comparing cognitive performance before and after a 12-hour shift, so more research is required on the impact of a 12-hour shift on cognitive performance in officers.\u003c/p\u003e\u003cp\u003eA second important factor that may be impacted by extended shift lengths is fatigue, though the research on fatigue, sleepiness, and alertness is also mixed. Vila et al., (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) suggested fatigue could increase fearfulness, irritability, and lead officers to make inappropriate decisions or engage in misconduct, and found fatigue can have a negative impact on worker health, safety, and performance (Vila, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Canadian police officers found higher levels of self-reported fatigue in officers on 12-hour shifts as opposed to 9-hour shifts (DeCarufel \u0026amp; Schaan, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) and research with US police officers found that 12-hour shifts are associated with greater sleepiness and less alertness than an 8- and 10-hour shift (Amendola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Furthermore, other studies have reported a significant decrease in stress and fatigue in officers following a switch to a 12-hour shift (Pierce \u0026amp; Dunham, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1992\u003c/span\u003e) or reported no difference between 8- to 12-hour shifts (Smith et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Most importantly, whilst there may be an increase in feelings of fatigue on longer shifts, this does not transfer to objective measures of fatigue (Smith et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1998\u003c/span\u003e), nor reductions in operational effectiveness (Amendola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Sundermeier, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOperational effectiveness of armed police officers is arguably the most important factor to consider in the context of shift length. Sundermeier (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) reported no reductions in performance in a Midwestern law enforcement agency, and Amendola et al., (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) found no differences between 8, 10 and 12-hour shifts in interpersonal interactions, shooting skills, and risky driving behaviours in a sample of over 200 US police officers. In fact, other factors may be more relevant. Blake and Cumella (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) found poor sleep quality, greater total time awake, more days worked, and working night or swing shifts as opposed to day shifts decreased the accuracy of police officers\u0026rsquo; decision making, particularly for ambiguous scenarios requiring inhibitory control (\u0026lsquo;no shoot scenarios\u0026rsquo;).\u003c/p\u003e\u003cp\u003eThe policing literature overwhelmingly relates to studies of armed US patrol officers that failed to find any effects on the use of force (although this was rarely measured directly). Given the differences between UK and US policing it is questionable whether this research evidence is directly applicable in the UK. However, the extremely low number of weapon discharges relative to the number of AFO deployments suggests that normal working practices do not routinely lead to the discharge of weapons. In the year ending March 2024, out of 7,589 firearms operations, there were only two incidents in which police firearms were intentionally discharged (Home Office, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The current study was therefore undertaken to identify whether a 12-hour shift affected the operational performance of armed police officers in the UK. Operational performance included measures of working memory, fatigue, sleepiness, and use of force decision-making. The hypotheses tested were that police officers would be affected by working a 12-hour shift. Specifically, it was hypothesised that self-reported fatigue and sleepiness would increase, and working memory capacity would decrease, after a 12-hour shift compared to before. It was also hypothesised that operational performance would not significantly differ after compared to before a 12-hour shift.\u003c/p\u003e"},{"header":"2. Materials and Method","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Design\u003c/h2\u003e\u003cp\u003eA within-subjects design was used to compare the operational performance of armed police officers immediately before, and immediately after an operational 12-hour shift.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Participants\u003c/h2\u003e\u003cp\u003eA sample of operational firearms officers were recruited via convenience sampling from three police forces across the United Kingdom. A sample size calculation in GPower 3.1 (Faul et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) indicated that a minimum sample size of \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;34 should be recruited to detect moderately sized differences, with a significance level set at \u003cem\u003eα\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.05 and power set at \u003cem\u003eβ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.80. The final sample consisted of 62 serving police officers which included 42 Armed Response Vehicle (ARV) officers, 19 Counter Terrorism Specialist Firearms Officers (CTSFO) and one Specialist Firearms Officer (SFO).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Measures\u003c/h2\u003e\u003cp\u003e\u003cem\u003eSamn-Perelli Fatigue Scale (\u003c/em\u003eSPS; Samn \u0026amp; Perelli, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1982\u003c/span\u003e). This scale is a commonly used measure of subjective fatigue. Participants are asked to respond to a single item asking how fatigued they feel using a scale ranging from 1 (fully alert, wide awake, \u0026lsquo;extremely peppy\u0026rsquo;) to 7 (completely exhausted, unable to function effectively, \u0026lsquo;ready to drop\u0026rsquo;).\u003c/p\u003e\u003cp\u003e\u003cem\u003eKarolinska Sleepiness Scale\u003c/em\u003e (KSS; Akerstedt \u0026amp; Gillberg, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). The KSS is a commonly used measure of situational sleepiness. Participants are asked to respond to a single item probing their current levels of sleepiness and alertness. The scale requires participants to rate their levels of sleepiness on a scale ranging from 1 (extremely alert) to 9 (very sleepy, great effort to feel alert, fighting sleep).\u003c/p\u003e\u003cp\u003e\u003cem\u003eOperational performance.\u003c/em\u003e Four scenarios were specifically developed by police firearms trainers in line with standard practice in UK firearms training. In each scenario, participants were individually briefed to respond to a situation where the police use of firearms might occur. In two scenarios, the appropriate and proportional use of force outcome was to not use force (i.e., \u0026lsquo;no shoot\u0026rsquo;), and in two scenarios the appropriate and proportional use of force outcome was to use force (i.e., \u0026lsquo;shoot\u0026rsquo;). Two firearms instructors observed the scenario, and one firearms instructor acted as the role player (i.e., a member of the public).\u003c/p\u003e\u003cp\u003eAll three instructors scored the scenario as a group immediately after the scenario had concluded. To score the scenario, a five-item scale was developed by the police training facilities. Instructors indicated on a 3-point scale (1\u0026thinsp;=\u0026thinsp;performed below expectations, 2\u0026thinsp;=\u0026thinsp;performed as expected, 3\u0026thinsp;=\u0026thinsp;performance exceeded expectations) how the participant scored on: (1) officer presence, (2) tactical movement; (3) Naturalistic Decision-Making (NDM) Assessment (escalation \u003cem\u003eor\u003c/em\u003e de-escalation of potential use of force) (4) communication/negotiation and (5) outcome (\u003cem\u003eappropriate\u003c/em\u003e use of force at the \u003cem\u003erelevant\u003c/em\u003e time; see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e below). Scores on all five scenario components were summed to create a total score for overall scenario performance, with higher scores reflecting better performance. It is important to note that for the NDM Assessment and outcome criterion, higher scores do not correspond to higher force but rather to an \u003cem\u003eappropriate\u003c/em\u003e management of force depending on the nature of the scenario (i.e., shoot or no-shoot).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u003cem\u003eScoring criteria and their descriptions for the scenarios.\u003c/em\u003e\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOfficer Presence\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDid the officer identify themselves as an Armed Police Officer?\u003c/p\u003e\u003cp\u003eDid they attempt to make face to face communication as soon as practicable?\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTactical Movement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDid the officer make best use of effective cover, move position to maintain communication without placing themselves in danger?\u003c/p\u003e\u003cp\u003eDid officers contain the subject?\u003c/p\u003e\u003cp\u003e\u0026lsquo;Blue on Blue\u0026rsquo;.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNDM Assessment (Escalation/de-escalation of potential use of force)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDid the officer respond to the communications and body movement appropriately (i.e. weapon position aim/off -aim/ready/south/not drawn)?\u003c/p\u003e\u003cp\u003eUse of force (consider less lethal options).\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCommunication/Negotiation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDid the officer communicate/negotiate at the appropriate level (i.e. Tone/volume/not repetitive/ clear and easily understood)?\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOutcome\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDid the officer use the appropriate force at the relevant time (i.e., shoot in the shoot scenario, and do not shoot in the no-shoot scenario)?\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eAutomated Operation Span Task\u003c/em\u003e (OSpan; Conway et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The OSpan was used as a measure of working memory capacity. In this task, participants are presented with a series of math problems (e.g., \u0026ldquo;8 * 3\u0026thinsp;+\u0026thinsp;2\u0026thinsp;=\u0026thinsp;32) which are followed by a letter sequence (e.g., \u0026ldquo;TLQ\u0026rdquo;). Participants are asked to decide whether the answer to the math problem is correct, and then recall the exact letter sequence using a letter matrix. The task consists of a practice session (22 trials) and a test session (15 trials). The practice session involves recalling short letter sequences, practicing the math task, and practicing combining the math problems with the letter sequence recall. The test session consists of 15 trials where each presents a math problem and a letter sequence made up of 3, 4, 5, 6, or 7 letters. The OSpan generates a total score for the \u0026lsquo;operation span\u0026rsquo; for each participant, which is the total number of letter sequences that participants could accurately remember in the test session. For example, if a participant correctly recalled 3 letters in a set size of 3, and 4 letters in a set size of 4, and 5 letters in a set size of 6, their operation span would be 3\u0026thinsp;+\u0026thinsp;4\u0026thinsp;+\u0026thinsp;0\u0026thinsp;=\u0026thinsp;7.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Procedure\u003c/h2\u003e\u003cp\u003eIn the first hour of a 12-hour shift, five participants entered a classroom and were given a participant ID code. Following an explanation of the study and information sheet, participants provided written informed consent, and responded to paper copies the sleepiness and fatigue scales. Next, participants completed the OSpan task via Inquisit software (Inquisit 5, 2016) on a Microsoft tablet. After completion of the task, participants individually took part in scenarios which were held in a firing range in the same building. There were four possible scenarios, which were counterbalanced. Each participant was briefed by the firearms instructor on the scenario and then entered the firearms range. In the range, there were two instructors observing the scenario, and one \u0026lsquo;stooge\u0026rsquo; instructor acting as a member of the public. On completion of the scenario, the participant was thanked and then asked to leave, and the three instructors scored the scenarios. Participants returned to repeat the testing procedure in the final hour of their shift. Scenarios were counterbalanced so participants would not take part in the same scenario at the start and end of their shift.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Data analysis\u003c/h2\u003e\u003cp\u003eScores for the fatigue and sleepiness scales, scenario performance and operation span task before and after a 12-hour shift were compared for all participants using parametric tests (i.e., paired sample t-test) for normally distributed and continuous data and non-parametric tests (i.e., Wilcoxon signed rank test) for non-normally distributed and/or ordinal-level data. Cohen\u0026rsquo;s d was used as the effect size for paired sample t-tests, \u003cem\u003er\u003c/em\u003e was calculated to estimate the effect size for Wilcoxon signed rank test. Because multiple comparisons were conducted, a Bonferroni correction was applied to correct for Type I errors (i.e., detecting a significant difference when there is none) which reduced the significance level to \u003cem\u003eα\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.013.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003e\u003cem\u003eSelf-reported fatigue\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eParticipants felt significantly more fatigued at the end of the shift compared to the start of the shift, \u003cem\u003eW\u003c/em\u003e = 745.00, Z = 3.44, \u003cem\u003ep\u003c/em\u003e \u0026lt; .001, \u003cem\u003er\u003c/em\u003e = .44, and this difference was moderate in size. \u0026nbsp;See table 2 for descriptive statistics.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSelf-reported sleepiness\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eParticipants reported higher levels of sleepiness at the end of the shift compared to the start of the shift, \u003cem\u003eW\u003c/em\u003e = 731.50, \u003cem\u003eZ\u0026nbsp;\u003c/em\u003e= 2.47, \u003cem\u003ep\u003c/em\u003e = .013, \u003cem\u003er\u003c/em\u003e = .31. This difference was moderate in size but only marginally significant.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eScenario performance\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThere was no significant difference in overall scenario performance between the end of the shift and the start of the shift, W = 478.00, \u003cem\u003eZ\u0026nbsp;\u003c/em\u003e= - 0.45, \u003cem\u003ep\u003c/em\u003e = .651, \u003cem\u003er\u003c/em\u003e = .06\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eWorking memory (operation span) \u003cstrong\u003e[1]\u003c/strong\u003e\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eParticipants had a greater operation span at the end of the shift compared to the start of the shift\u003cem\u003e, t\u003c/em\u003e(60) = -3.51, \u003cem\u003ep\u003c/em\u003e \u0026lt; .001, \u003cem\u003ed\u003c/em\u003e = 0.45, and this difference was small in size. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 2. \u003cem\u003eDescriptive statistics for fatigue, sleepiness, scenario performance and operation span before and after the 12-hour shift.\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 26px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 37px;\"\u003e\n \u003cp\u003eAt the start of the shift\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 0px;\"\u003e\n \u003cp\u003eAt the end of the shift\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 26px;\"\u003e\n \u003cp\u003eFatigue\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 37px;\"\u003e\n \u003cp\u003e3.00 (5.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 0px;\"\u003e\n \u003cp\u003e4.00 (5.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 26px;\"\u003e\n \u003cp\u003eSleepiness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 37px;\"\u003e\n \u003cp\u003e3.00(7.00)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 0px;\"\u003e\n \u003cp\u003e4.00(7.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 26px;\"\u003e\n \u003cp\u003eOperation span\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 37px;\"\u003e\n \u003cp\u003e38.21(16.06)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 0px;\"\u003e\n \u003cp\u003e44.90(16.40)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 26px;\"\u003e\n \u003cp\u003eScenario performance\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 37px;\"\u003e\n \u003cp\u003e10.00(10.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 0px;\"\u003e\n \u003cp\u003e11.00(7.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cem\u003eNote: Scores are measured on a scale ranging from 1 - 7 (fatigue), 1 - 9 (sleepiness), 0 - 75 (Operation span), and 5 - 15 (Scenario performance). Values for operation span are mean and standard deviation (\u0026plusmn;SD). Values for fatigue, sleepiness, and scenario performance are median and range.\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cdiv id=\"ftn1\"\u003e\n \u003cp\u003e[1] One participant indicated they did not understand the task and their corresponding data was subsequently coded as missing for this analysis. \u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThis is the first study to measure the impact of shift length on the operational performance of AFOs in the UK. Results showed that there was a significant increase in self-reported fatigue and a marginally significant increase in sleepiness at the end of an operational 12-hour shift. There was a potentially paradoxical significant increase in working memory capacity at the end of the 12-hour shift. The training scenario performance, which was used to measure operational effectiveness including appropriate use of force, was not significantly affected by a 12-hour operational shift despite the increased self-reported fatigue and sleepiness. The results therefore suggest that police officers are able to respond appropriately to a (potential) armed confrontation at the end of a 12-hour shift despite self-reporting greater levels of fatigue and sleepiness.\u003c/p\u003e\u003cp\u003eThe \u0026lsquo;common sense\u0026rsquo; view is that a 12-hour shift should affect AFO performance, however the available literature often does not support that opinion. Armed police officers in this study were, however, more fatigued and sleepier at the end of a 12-hour shift, which is generally supported in the literature. Amendola et al., (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) similarly found higher levels of sleepiness and alertness in US police officers that worked 12-hour, as opposed to 10-hour or 8-hour shifts, and deCarufel and Schaan (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) reported similar findings in Canadian police officers when comparing 12-hour and 9-hour shifts. Some research has found no differences (Smith et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1998\u003c/span\u003e), or even a reduction in fatigue in officers following a switch to a 12-hour shift (Pierce \u0026amp; Dunham, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1992\u003c/span\u003e) which does not align to our findings. This may be explained by individuals on shorter shifts getting less sleep and having poorer sleep quality, and total time awake has been linked with a reduction in police officer decision making (Blake \u0026amp; Cumella, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). It is also important to consider the preferences of police officers when introducing any changes to shift length policy, for example, despite officers in deCarufel and Schaan\u0026rsquo;s (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) study reporting greater fatigue, they did not wish to return to an 8-hour shift given their preference for a 12-hour shift schedule. Furthermore, whilst armed police officers in the current study were more fatigued and sleepy, this did not transfer to objective measures of performance in line with previous research (Amendola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Sundermeier, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe operational effectiveness of armed police officers in the current study, as measured by the training scenario performance, was not affected by a 12-hour operational shift. These scenarios tested the appropriate and proportional use of force (if necessary) using scripted live role plays and were designed to test whether the participants were able to function effectively in their role. This meant that in two scenarios the participants were required to discharge their weapon systems to neutralise the threat posed by the role player and in two they were not. The results therefore suggest that police officers are able to respond appropriately to a (potential) armed confrontation at the end of a 12-hour shift despite self-reporting greater levels of fatigue and sleepiness. This supports research by Amendola et al., (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) that found no differences between 8, 10 and 12-hour shifts in interpersonal interactions, shooting skills, and risky driving behaviours in a sample of over 200 US police officers, and by Sundermeier (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) that reported no reductions in performance in a Midwestern law enforcement agency. Given that the policing literature overwhelmingly relates to studies of armed US patrol officers, and there are significant differences between UK and US policing, there is a need to understand whether these findings translate to UK policing. Whilst all police officers in the US carry firearms while on duty, in the UK only 3.9% of the total number of police officers are armed (Home Office, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The current findings demonstrate that the failure to find effects on the use of force in US officers does generalise to UK armed police officers. This aligns to real use of force decisions which shows in 2024, out of 7,589 firearms operations, there were only two incidents in which police firearms were intentionally discharged (Home Office, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Thus, normal working practices do not seem to routinely lead to the discharge of weapons.\u003c/p\u003e\u003cp\u003eThe findings of this study suggest that whilst there was an increase in fatigue and sleepiness, paradoxically there was also a small increase in cognitive performance. Working memory was measured using the OSpan, which is designed to measure the capacity to maintain and manipulate information in working memory while performing other tasks (Conway et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The literature is mixed with regards to the impact of shift length on cognitive performance. Whilst some studies indicate lower cognitive performance during 12-hour vs 8-hour shifts in non-policing industries (Rosa \u0026amp; Bonnet, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Rosa \u0026amp; Colligan, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1992\u003c/span\u003e), or at the end as opposed to the start of a 12-hour shift (Kazemi et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), other research found no differences (Bernreuter, \u0026amp; Sullivan, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Schroeder, Rosa, \u0026amp; Witt, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Amenadola et al., (2011) also found no differences in the cognitive performance of police officers in the US between different shift lengths. However, these studies did not find a positive increase in cognitive performance. Whilst the findings of the current study, that working memory capacity increased may seem unexpected, the literature suggests that the link between shift length and cognitive may be more nuanced. Anaesthesiology residents showed a significant improvement in working memory after, compared to before working a 24-hour shift, and concentration did not diminish (Tadinac et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Therefore, some cognitive functions may improve or remain unaffected, which may explain the increase in working memory in our study. A second explanation could be that the increase in cognitive performance is due to practice effects. A study by Taylor et al., (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) found practice effects for several working memory tests in a study on the impact of fatigue on cognitive performance in UK police officers during a forward rotating shift pattern. Similar learning effects have been observed in non-policing samples in relation to working memory and mental fatigue (Pergher et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Future research is required to better tease apart the reasons for an increase in cognitive performance in this study.\u003c/p\u003e\u003cp\u003eThese findings have potential policy implications. In the aftermath of the Anthony Grainger Inquiry (Home Office, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), the NPCC and College of Policing were tasked with deciding whether there should be a maximum period during which AFOs are permitted to remain on continuous duty. Furthermore, the Police Federation states that shift length should ideally be between 8\u0026ndash;10 hours, and do not recommend 12 hour shifts due to health and safety concerns. The findings of this experiment contradict this recommendation and indicate that whilst there may be an increase in fatigue and sleepiness, there is also potentially a small increase in cognitive performance, and no impact on the operational effectiveness of armed police officers. Our findings suggest that armed police officers are not more likely to discharge their weapon inappropriately at the end of a 12-hour shift. Furthermore, it is important to take police officers shift preferences into account when making policy changes, as deCarufel \u0026amp; Schaan (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e) found officers preferred a 12-hour shift compared to 8-hour shift length. Furthermore, whilst not significant, officers working 12-hour shifts reported higher levels of sleep and worked less overtime than those on 8-hour shifts (Amendola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Future research could be conducted to understand officers\u0026rsquo; preferences different shift lengths, and how these impact their perceived levels of stress, and account for the impact on overall sleep levels. Blake and Cumella (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) found police officers with poor sleep quality and greater total time awake made more inaccurate use of force decisions, particularly when presented with no-shoot and ambiguous scenarios, so the recommendation that police work 8-hour shifts may be counter-intuitive. It is possible that there is a sweet spot, as Amendola et al., (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) found a 10-hour shift was the most effective shift length, though future research with UK armed police officers would need to investigate this further.\u003c/p\u003e\u003cp\u003eOur study has several strengths and limitations. The study is novel, providing the first preliminary evidence that the operational performance of AFOs in the UK is not significantly negatively impacted by a 12-hour shift. Armed police officers in the current study were tested immediately before, and after an operational shift, and responded to a live fire exercise, where two instructors observed the scenario, and one \u0026lsquo;stooge\u0026rsquo; instructor acted as a member of the public. The armed police officers in the experiment needed to decide on the appropriate use of force (i.e., a shoot or no-shoot) depending on the nature of the scenario, using blank firing weapons. In contrast to previous research in this area, that either used computer-based decisions on the use of force (Blake \u0026amp; Cumella, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) or required police officers to respond to a video-based simulator (Amendola et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), the current study is more ecologically valid.\u003c/p\u003e\u003cp\u003eHowever, it is important to note that this study, like every other study of this nature, has some limitations that need to be considered. The sample size was not large enough to detect small effects, and the non-significant differences in operational performance may be attributable to the use of non-parametric tests, which typically reduce the likelihood of detecting significant differences. However, given that the results of this study suggest a non-significant increase in operational performance after the shift, the inability to detect small effects does not indicate that operational performance would decrease post-shift. It is however possible that a 12-hour shift could cause problems for individual participants because of what happens on that shift, and individual and situational factors could influence decision-making in high stake environments. Therefore, it is not possible to emphatically state that shift length will not cause a performance decrement for every armed officer in the UK on every shift. Even though undetected differences may be small in statistical terms, they could have a potentially detrimental impact considering the context. In addition to this, to keep with the applied nature of the study, standard scoring procedures were used that were developed by training officers for this type of training exercise. The range of scores for the scenario outcome was small, partly due to the rating scale used. A more refined scoring procedure would have allowed for more advanced statistical analysis and may have identified fine grained effects in terms of operational performance, but the unfamiliarity of the training staff in using that scoring system may have caused more problems than it solved. In the absence of a universally agreed method of scoring scenarios of this type it is not possible to determine the impact of the system used on the results obtained. Furthermore, the current study tested AFO performance in training scenarios. Although the scenarios were designed by experienced firearms trainers and are highly similar to the scenarios used in AFO training, it is possible that AFO performance in real (potential) armed confrontations is impacted differently compared to AFO performance in training scenarios. Lastly, the study design did not allow comparing performance between \u0026lsquo;shoot\u0026rsquo; and \u0026lsquo;no-shoot\u0026rsquo; scenarios. The current findings therefore cannot indicate whether shift length specifically affects decision-making in situations that require inhibitory control, which are precisely scenarios that could lead to inappropriate use of (potentially lethal) force. While the current results suggest that operational performance is not affected, future research should disentangle the effect of shift length on different scenario types. Given that Blake and Cumella (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) found police officers with poorer sleep quality, greater total time awake, more days worked, and working night or swing shifts had less accurate decision-making particularly in no-shoot scenarios, future research teasing apart the impact of a 12-hour shift length on scenario type would be beneficial.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThe results of this study suggest that a 12-hour shift increases self-reported fatigue and sleepiness but does not affect the actual performance of armed police officers. There was no evidence that (potentially lethal) force was used more inappropriately after, as opposed to before a 12-hour shift. Potential smaller effects of 12-hour shifts on AFO performance could be tested in future with larger samples.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe also sincerely appreciate the support of the three police forces for facilitating the study\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eEthical Approval\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThis study received ethical approval from the University of Liverpool's Research Ethics Committee (Approval No: 8638). All research activities were conducted in full compliance with the University’s Ethical Review Policy and in accordance with the principles of the Declaration of Helsinki. Prior to participation, all participants provided written informed consent after receiving comprehensive information about the study’s aims, procedures, confidentiality safeguards, voluntary nature of participation, and their right to withdraw at any time without penalty.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eFunding\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Police Chief’s Council.\u003c/p\u003e\n\u003cp\u003e\u003cu\u003eAvailability of data and materials\u0026nbsp;\u003c/u\u003e\u003c/p\u003e\n\u003cp\u003eData are available upon reasonable request. Data from this study will be made available upon reasonable request by contacting the corresponding author at [email protected]. Data will be made available for 10 years in line with ethical considerations.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAmendola, K. L., Weisburd, D., Hamilton, E. E., Jones, G., \u0026amp; Slipka, M. (2011). An experimental study of compressed work schedules in policing: Advantages and disadvantages of various shift lengths. \u003cem\u003eJournal of Experimental Criminology, 7\u003c/em\u003e, 407\u0026ndash;442. https://www.policinginstitute.org/wp-content/uploads/2015/06/Amendola-et-al.-2011-The-Impact-of-Shift-Length-Full-Report-.pdf\u003c/li\u003e\n\u003cli\u003eAkerstedt, T., \u0026amp; Gillberg, M. (1990). Subjective and objective sleepiness in the active individual. \u003cem\u003eInternational Journal of Neuroscience, 52\u003c/em\u003e, 29\u0026ndash;37. https://doi.org/10.3109/00207459008994241\u003c/li\u003e\n\u003cli\u003eBernreuter, M., \u0026amp; Sullivan, M. (1995). Survey and critique of studies related to shift length variations in nursing from 1970 to 1993. \u003cem\u003eInternational Journal of Nursing Studies, 32\u003c/em\u003e(2), 188\u0026ndash;197. https://doi.org/10.1016/0020-7489(94)00026-G\u003c/li\u003e\n\u003cli\u003eBlake, D., \u0026amp; Cumella, E. (2015). Factoring fatigue into police deadly force encounters: Decision-making and reaction times. \u003cem\u003eLaw Enforcement Executive Forum, 15\u003c/em\u003e(1), 44\u0026ndash;65.\u003c/li\u003e\n\u003cli\u003eCollege of Policing. (2013). \u003cem\u003eArmed policing\u003c/em\u003e. https://www.college.police.uk/app/armed-policing\u003c/li\u003e\n\u003cli\u003eConway, A. R. A., Kane, M. J., Bunting, M. F., Hambrick, D. Z., Wilhelm, O., \u0026amp; Engle, R. W. (2005). Working memory span tasks: A methodological review and user\u0026rsquo;s guide. \u003cem\u003ePsychonomic Bulletin \u0026amp; Review, 12\u003c/em\u003e(5), 769\u0026ndash;786.\u003c/li\u003e\n\u003cli\u003eDeCarufel, A., \u0026amp; Schaan, J. L. (1990). The impact of compressed work weeks on police job involvement. \u003cem\u003eCanadian Police College Journal\u003c/em\u003e. https://www.ojp.gov/ncjrs/virtual-library/abstracts/impact-compressed-work-weeks-police-job-involvement\u003c/li\u003e\n\u003cli\u003eFaul, F., Erdfelder, E., Buchner, A., \u0026amp; Lang, A. (2009). Statistical power analyses using G*Power 3.1: Tests for correlation and regression analysis. \u003cem\u003eBehavior Research Methods, 41\u003c/em\u003e, 1149\u0026ndash;1160.\u003c/li\u003e\n\u003cli\u003eHome Office. (2019). \u003cem\u003eAntony Grainger inquiry: Report into the death of Anthony Grainger\u003c/em\u003e. https://www.gov.uk/government/publications/anthony-grainger-inquiry-report-into-the-death-of-anthony-grainger\u003c/li\u003e\n\u003cli\u003eHome Office. (2024). \u003cem\u003ePolice use of firearms statistics, England and Wales: April 2023 to March 2024\u003c/em\u003e. https://www.gov.uk/government/statistics/police-use-of-firearms-statistics-april-2023-to-march-2024\u003c/li\u003e\n\u003cli\u003eInquisit 5 [Computer software]. (2016). Millisecond Software. https://www.millisecond.com\u003c/li\u003e\n\u003cli\u003eKazemi, R., Haidarimoghadam, R., Motamedzadeh, M., Golmohamadi, R., Soltanian, A., \u0026amp; Zoghipaydar, M. R. (2016). Effects of shift work on cognitive performance, sleep quality, and sleepiness among petrochemical control room operators. \u003cem\u003eJournal of Circadian Rhythms, 14\u003c/em\u003e(1). https://doi.org/10.5334/jcr.134\u003c/li\u003e\n\u003cli\u003eLeso, V., Fontana, L., Caturano, A., Vetrani, I., Fedele, M., \u0026amp; Iavicoli, I. (2021). Impact of shift work and long working hours on worker cognitive functions: Current evidence and future research needs. \u003cem\u003eInternational Journal of Environmental Research and Public Health, 18\u003c/em\u003e(12), 6540. https://doi.org/10.3390/ijerph18126540\u003c/li\u003e\n\u003cli\u003eLockley, S. W., Cronin, J. W., Evans, E. E., Cade, B. E., Lee, C. J., Landrigan, C. P., ... \u0026amp; Czeisler, C. A. (2004). Effect of reducing interns\u0026apos; weekly work hours on sleep and attentional failures. \u003cem\u003eNew England Journal of Medicine, 351\u003c/em\u003e(18), 1829\u0026ndash;1837. https://doi.org/10.1056/NEJMoa041404\u003c/li\u003e\n\u003cli\u003ePergher, V., Vanbilsen, N., \u0026amp; Van Hulle, M. (2021). The effect of mental fatigue and gender on working memory performance during repeated practice by young and older adults. \u003cem\u003eNeural Plasticity, 2021\u003c/em\u003e, Article 6612805. https://doi.org/10.1155/2021/6612805\u003c/li\u003e\n\u003cli\u003ePierce, J. L., \u0026amp; Dunham, R. B. (1992). The 12-hour work day: A 48-hour, eight-day week. \u003cem\u003eAcademy of Management Journal, 35\u003c/em\u003e(5), 1086\u0026ndash;1098.\u003c/li\u003e\n\u003cli\u003eRosa, R. R., \u0026amp; Bonnet, M. H. (1993). Performance and alertness on 8 h and 12 h rotating shifts at a natural gas utility. \u003cem\u003eErgonomics, 36\u003c/em\u003e(10), 1177\u0026ndash;1193. https://doi.org/10.1080/00140139308967987\u003c/li\u003e\n\u003cli\u003eRosa, R. R., \u0026amp; Colligan, M. J. (1992). Application of a portable test battery in the assessment of fatigue in laboratory and worksite studies of 12-hour shifts. \u003cem\u003eScandinavian Journal of Work, Environment \u0026amp; Health\u003c/em\u003e, 113\u0026ndash;115. http://www.jstor.org/stable/40966090\u003c/li\u003e\n\u003cli\u003eSamn, S. W., \u0026amp; Perelli, L. P. (1982). Estimating aircrew fatigue: A technique with implications to airlift operations (SAM-TR-82-21). USAF School of Aerospace Medicine.\u003c/li\u003e\n\u003cli\u003eSchroeder, D. J., Rosa, R. R., \u0026amp; Witt, L. A. (1998). Some effects of 8-vs. 10-hour work schedules on the test performance/alertness of air traffic control specialists. \u003cem\u003eInternational Journal of Industrial Ergonomics, 21\u003c/em\u003e(3\u0026ndash;4), 307\u0026ndash;321. https://doi.org/10.1016/S0169-8141(97)00044-9\u003c/li\u003e\n\u003cli\u003eSmith, L., Folkard, S., Tucker, P., \u0026amp; MacDonald, I. (1998). Work shift duration: A review comparing eight hour and 12 hour shift systems. \u003cem\u003eOccupational and Environmental Medicine, 55\u003c/em\u003e(4), 217\u0026ndash;229. https://doi.org/10.1136/oem.55.4.217\u003c/li\u003e\n\u003cli\u003eSundermeier, J. (2008). A look at the 12-hour shift: The Lincoln police department study. \u003cem\u003eThe Police Chief, 75\u003c/em\u003e(3). https://www.ojp.gov/ncjrs/virtual-library/abstracts/look-12-hour-shift-lincoln-police-department-study\u003c/li\u003e\n\u003cli\u003eTadinac, M., Ante, S., Ivana, H., Branka, M. S., \u0026amp; Romina, I. (2014). Age and individual sleep characteristics affect cognitive performance in anesthesiology residents after a 24-hour shift. \u003cem\u003eActa Clinica Croatica, 53\u003c/em\u003e(1), 22\u0026ndash;30. https://hrcak.srce.hr/126143\u003c/li\u003e\n\u003cli\u003eTaylor, Y., Merat, N., \u0026amp; Jamson, S. (2019). The effects of fatigue on cognitive performance in police officers and staff during a forward rotating shift pattern. \u003cem\u003eSafety and Health at Work, 10\u003c/em\u003e(1), 67\u0026ndash;74. https://doi.org/10.1016/j.shaw.2018.08.003\u003c/li\u003e\n\u003cli\u003eVila, B. J., Kenney, D. J., Morrison, G. B., \u0026amp; Reuland, M. (2000). Evaluating the effects of fatigue on police patrol officers: Final report. \u003cem\u003ePolice Executive Research Forum\u003c/em\u003e. https://www.ojp.gov/pdffiles1/nij/grants/184188.pdf\u003c/li\u003e\n\u003cli\u003eVila, B. J. (2006). Impact of long work hours on police officers and the communities they serve. \u003cem\u003eAmerican Journal of Industrial Medicine, 49\u003c/em\u003e(11), 972\u0026ndash;980. https://doi.org/10.1002/ajim.20333\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Armed policing, Shift length, Lethal force, Working memory, Fatigue","lastPublishedDoi":"10.21203/rs.3.rs-7272614/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7272614/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Police Federation do not recommend 12-hour shifts yet the impact of shift length on cognition, sleepiness, fatigue, and operational effectiveness is largely unknown. A study on the effects of a 12-hour operational shift on armed police officers was conducted with three UK Police Forces. A total of 62 officers were tested from a variety of roles (armed response vehicle crew, specialist firearms officer, and counter terrorism specialist firearms officer). Psychological measures tested levels of fatigue, sleepiness, and working memory, and a training scenario measured operational effectiveness including appropriate use of force at the beginning and end of a shift. Participants showed a significant increase in fatigue, sleepiness, and cognitive performance at the end of the shift. There was no effect on training scenario performance, suggesting that a 12-hour shift does not have an effect on the ability of armed police officers to respond appropriately to a potential armed confrontation.\u003c/p\u003e","manuscriptTitle":"The impact of shift length on the operational effectiveness of UK Authorised Firearms Officers: a field experimental study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-05 10:38:19","doi":"10.21203/rs.3.rs-7272614/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ce854f5e-d880-496a-9be7-9cbcc0dfb5f6","owner":[],"postedDate":"September 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-01T00:23:56+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-05 10:38:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7272614","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7272614","identity":"rs-7272614","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}