Meta-analysis of e-cigarette price elasticity

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Understanding whether and how much ENDS act as economic substitutes for cigarettes helps inform tobacco policy to minimize harm. The goals of this study are to review the own-price elasticity of ENDS, the cross-price elasticity of ENDS with respect to cigarette price (including taxes), and the cross-price elasticity of cigarettes with respect to ENDS price. Methods: This systematic review and meta-analysis followed Cochrane review guidelines where applicable. Articles were sourced from PubMed and Google Scholar; inclusion criteria were primary sources of all study designs and groups of participants with relevant elasticity outcomes. Where appropriate, effects were combined in random-effects models with the two-step DerSimonian and Laird estimator. Other articles were reviewed narratively. Results: 23 studies were retained. 13 were appropriate for meta-analysis. A 10% increase in ENDS price is associated with an 11.5% (9.7%–13.4%) decrease in ENDS sales/purchases, and also decreased ENDS use prevalence. A 10% increase in cigarette price is associated with a 9.8% (5.7%–13.8%) increase in ENDS sales/purchases, and also increased ENDS use prevalence. A 10% increase in ENDS price is non-significantly associated with a 1.1% (-0.5%–2.8%) increase in cigarette sales/purchases, and increased ENDS price was associated with increased smoking prevalence, propensity, and number of cigarettes smoked. Discussion: These data suggest ENDS are substitutes for cigarettes. Taxing cigarettes encourages switching away from smoking. More research is needed to clarify the association between ENDS price and cigarette demand. Results are limited by imprecision due to low number of studies. Conclusions: Policymakers should consider using taxation to influence behavior and tax tobacco products in proportion to their harm. Registration: OSF." } { "@context": "http://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": "1", "item": { "@id": "https://f1000research.com/", "name": "Home" } }, { "@type": "ListItem", "position": "2", "item": { "@id": "https://f1000research.com/browse/articles", "name": "Browse" } }, { "@type": "ListItem", "position": "3", "item": { "@id": "https://f1000research.com/articles/12-121/v1", "name": "Meta-analysis of e-cigarette price elasticity" } } ] } Home Browse Meta-analysis of e-cigarette price elasticity ALL Metrics - Views Downloads Get PDF Get XML Cite How to cite this article Selya A, Foxon F, Chandra S and Nealer E. Meta-analysis of e-cigarette price elasticity [version 1; peer review: peer review discontinued] . F1000Research 2023, 12 :121 ( https://doi.org/10.12688/f1000research.129233.1 ) NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article. Close Copy Citation Details Export Export Citation Sciwheel EndNote Ref. Manager Bibtex ProCite Sente EXPORT Select a format first Track Share ▬ ✚ Systematic Review Meta-analysis of e-cigarette price elasticity [version 1; peer review: peer review discontinued] Arielle Selya https://orcid.org/0000-0001-7026-6988 1 , Floe Foxon https://orcid.org/0000-0002-4893-9178 1 , Siddharth Chandra 1 , Erin Nealer 1 Arielle Selya https://orcid.org/0000-0001-7026-6988 1 , Floe Foxon https://orcid.org/0000-0002-4893-9178 1 , Siddharth Chandra 1 , Erin Nealer 1 PUBLISHED 02 Feb 2023 Author details Author details 1 PinneyAssociates, Inc., Pittsburgh, Pennsylvania, USA Arielle Selya Roles: Conceptualization, Data Curation, Formal Analysis, Writing – Original Draft Preparation Floe Foxon Roles: Conceptualization, Data Curation, Formal Analysis, Methodology, Software, Visualization, Writing – Original Draft Preparation Siddharth Chandra Roles: Formal Analysis, Methodology, Supervision, Writing – Review & Editing Erin Nealer Roles: Data Curation, Project Administration, Supervision, Writing – Review & Editing OPEN PEER REVIEW PEER REVIEW DISCONTINUED Abstract Background: Adoption of electronic nicotine delivery systems (ENDS) has the potential to impact the prevalence of combusted cigarette use. Understanding whether and how much ENDS act as economic substitutes for cigarettes helps inform tobacco policy to minimize harm. The goals of this study are to review the own-price elasticity of ENDS, the cross-price elasticity of ENDS with respect to cigarette price (including taxes), and the cross-price elasticity of cigarettes with respect to ENDS price. Methods: This systematic review and meta-analysis followed Cochrane review guidelines where applicable. Articles were sourced from PubMed and Google Scholar; inclusion criteria were primary sources of all study designs and groups of participants with relevant elasticity outcomes. Where appropriate, effects were combined in random-effects models with the two-step DerSimonian and Laird estimator. Other articles were reviewed narratively. Results: 23 studies were retained. 13 were appropriate for meta-analysis. A 10% increase in ENDS price is associated with an 11.5% (9.7%–13.4%) decrease in ENDS sales/purchases, and also decreased ENDS use prevalence. A 10% increase in cigarette price is associated with a 9.8% (5.7%–13.8%) increase in ENDS sales/purchases, and also increased ENDS use prevalence. A 10% increase in ENDS price is non-significantly associated with a 1.1% (-0.5%–2.8%) increase in cigarette sales/purchases, and increased ENDS price was associated with increased smoking prevalence, propensity, and number of cigarettes smoked. Discussion: These data suggest ENDS are substitutes for cigarettes. Taxing cigarettes encourages switching away from smoking. More research is needed to clarify the association between ENDS price and cigarette demand. Results are limited by imprecision due to low number of studies. Conclusions: Policymakers should consider using taxation to influence behavior and tax tobacco products in proportion to their harm. Registration: OSF . READ ALL READ LESS Keywords E-Cigarette, Vaping, Cigarette, Smoking, Elasticity, Own-Price, Cross-Price, Meta-Analysis Corresponding Author(s) Floe Foxon ( [email protected] ) Close Corresponding author: Floe Foxon Competing interests: Through PinneyAssociates, Inc. all authors provide consulting services on tobacco harm reduction on an exclusive basis to Juul Labs, Inc. Funding for these analyses was provided by Juul Labs, Inc. Juul Labs, Inc. commented on a draft of the manuscript, but did not otherwise participate in study execution, data analysis, writing, or decision to publish. Grant information: Funding for these analyses was provided by Juul Labs, Inc. Juul Labs, Inc. commented on a draft of the manuscript, but did not otherwise participate in study execution, data analysis, writing, or decision to publish. Copyright: © 2023 Selya A et al . This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. How to cite: Selya A, Foxon F, Chandra S and Nealer E. Meta-analysis of e-cigarette price elasticity [version 1; peer review: peer review discontinued] . F1000Research 2023, 12 :121 ( https://doi.org/10.12688/f1000research.129233.1 ) First published: 02 Feb 2023, 12 :121 ( https://doi.org/10.12688/f1000research.129233.1 ) Latest published: 02 Feb 2023, 12 :121 ( https://doi.org/10.12688/f1000research.129233.1 ) Introduction Electronic nicotine delivery systems (ENDS) are nicotine products that electronically heat a nicotine-containing solution into aerosol for inhalation. Unlike cigarettes, ENDS do not involve combustion, so ENDS users are exposed to much lower levels of harmful constituents. 1 , 2 Thus, ENDS are considered to have potential for harm reduction among adults who would otherwise smoke. 3 However, the impact of ENDS use on smoking behavior is debated. In the US, youth use of ENDS remains a concern 4 – though down more than 50% from its peak in 2019 5 – raising worries that ENDS use may lead to nicotine addiction 6 and initiation of cigarette smoking, 7 , 8 for those who would not otherwise have smoked. Among adults who smoke, there exists general consensus that ENDS use likely reduces harm for those who switch completely away from smoking, 1 , 2 however concerns have been raised that ENDS use might prolong smoking among those who might otherwise have quit, 9 or lead to heavier cigarette smoking. 10 These concerns are lessened by studies examining relationships between ENDS and cigarette use at the aggregate or population level. Smoking prevalence among youth declined faster after ENDS became widely available, 11 – 14 suggesting ENDS may have diverted nicotine-seeking youth away from cigarette smoking. Similarly, smoking rates have declined more sharply among adults after ENDS became available, 15 – 17 particularly among younger adults with higher rates of ENDS use. Quasi-experimental economic studies also show an inverse relationship between cigarette smoking and ENDS use. 18 , 19 Together, these studies suggest that ENDS are offsetting or replacing cigarettes, rather than augmenting the population prevalence of any nicotine use. An understanding of how ENDS use impacts cigarette smoking behavior is essential for effective and well-informed tobacco policy. Some recent policies, e.g., flavor bans, have focused on restricting ENDS products, motivated out of a desire to protect youth. Unfortunately, such policies can have unintended consequences of increasing cigarette smoking in youth 18 and adults 20 when the possible interrelationship between cigarettes and ENDS is not considered. One such restriction on ENDS products is taxation of ENDS products. A potential consequence of such taxes may be substitution between ENDS and cigarettes. In microeconomics, two products may be substitutes if one product replaces the other in use as a result of changed conditions (e.g. a change in price/availability of one of the products). 21 A rich source of data on potential substitution between tobacco products is economic studies of the effect of price changes for a tobacco product on the use of or demand for that same product (“own-price elasticity”) or another tobacco product (“cross-price elasticity”). Advantages of these studies are that they capture aggregate-level behavior in real-world settings, in response to specific policy actions (e.g. taxes). Analyses of Nielsen data suggest that taxes on cigarettes and ENDS are passed through completely to consumer prices. 22 , 23 This is quantified by the “pass-through fraction”, which is the fraction of a tax on manufacturers or retailers that is passed on to the consumer. Therefore, on the average, changes in taxes act like changes in price for these products, meaning studies on price and tax change can inform about their potential substitution. Concerning the price elasticities of cigarettes and ENDS, a systematic review and meta-analysis was published previously, 24 and reported consistent substitution effects between these products, as well as between cigarettes and other non-cigarette tobacco products. The present analysis expands on the previously published study in the following ways. First, the previous study included only five studies on ENDS price elasticity, whereas the present analysis features more than 20. Many of these studies are from more recent years when the ENDS market size was substantially larger, 25 and includes newer-generation ENDS products than the studies reviewed by the previous study in 2018. Second, although the previous study reports on the cross elasticity of ENDS with respect to cigarette price, it did not report on the cross elasticity of cigarettes with respect to ENDS price. The current study presents a systematic review and meta-analysis of ENDS price elasticities. The research questions addressed are: 1) what is the effect of ENDS price changes on the use of or demand for ENDS (own-price elasticity of ENDS)?; 2) what is the effect of cigarette price changes on the use of or demand for ENDS (cross-price elasticity of ENDS with respect to cigarettes)?; and 3) what is the cross-price elasticity of cigarettes with respect to ENDS? The first question acts to legitimize the methods implemented in the main analyses, while questions 2 and 3 serve to inform on the potential impact of ENDS policy actions. Because of the high pass-through fraction for ENDS and cigarettes, 22 , 23 changes in either price or tax are considered equivalently in the present study. Methods Data This meta-analysis was registered with the Center for Open Science’s OSF Registries on January 20, 2022 ( https://doi.org/10.17605/OSF.IO/9HBWQ ), following Cochrane guidelines for systematic reviews where applicable ( https://training.cochrane.org/handbook ). This pre-registration was based on updating the results of the previously published study 24 (research questions 1 and 2 above), and while conducting the present research a number of results on the cross-price elasticity of cigarettes with respect to ENDS price (question 3, the inverse of research question 2 above) were found. Thus, we extended the pre-registration following the same methods as pre-registered analyses for research question 3 above. Studies on tobacco product elasticity were sourced from peer-reviewed publications and National Bureau of Economic Research (NBER) working papers in the PubMed and Google Scholar databases using the two separate search terms ‘e-cigarette’ + ‘own-price’, and ‘e-cigarette’ + ‘cross-price’. Pre-registration authors independently screened search results for eligibility in blinded and duplicate fashion. Conflicts were resolved through discussion. The inclusion criteria were primary sources of all study designs and groups of participants with relevant elasticity outcomes. No limits were applied to date of publication or language; regardless, all articles retained for review were in English. Studies on elasticity examined how changes in price (or tax, which, due to a high pass-through fraction, is equivalent to a change in price 22 , 23 ), of a product impacted one of two measures of demand. 1. Quantity of cigarettes or ENDS sold/purchased. This was examined in the literature through both commercial retail/market-level models and hypothetical purchasing experiments. Market-level models use real-world retail-level data, often provided by Nielsen, in regressions which relate price to sales volume. Hypothetical purchasing experiments require participants to complete virtual market tasks involving different products at different prices, and to indicate which or how many they would prefer. 2. Prevalence, frequency, or quantity of cigarette or ENDS use. This was examined in the literature through hypothetical purchasing experiments such as discrete choice experiments, and models relating price to said outcomes as measured in surveys. Data were extracted manually by reviewing the full text of each manuscript, including the geographic region, age group (adults/adolescents), ENDS product type (disposable; reusable/rechargeable; liquid/cartridges; or multiple), price elasticity type (own/cross), effect size (elasticity value), 95% confidence interval (CI), standard errors (SEs), and p-values. When multiple models were presented in a single study with a range of independent control variables, results were taken from the model with the most controls for the most realistic estimate (typically the ‘main result’). Where effects were not reported in the original texts, estimates were derived from figures. Where only SEs were reported, Wald-type 95% CIs were estimated as CI = effect size ± 1.95996 × standard error . Similarly, where only CIs were reported, SEs were estimated conservatively as standard error = max LCL − effect size − 1.95996 UCL − effect size 1.95996 . Because the underlying studies do not always report what kind of distribution their SEs are based on, we assume a normal distribution of SEs. Where only p-values were reported, SEs and CIs were conservatively estimated following the methodology of Altman and Bland. 26 Elasticities expressed on the scale α = e elasticity were transformed by taking the natural logarithm ( elasticity = ln α ). Statistical analysis Meta-analytic summary statistics were estimated via a method of moments random-effects model with the two-step DerSimonian and Laird estimator. 27 A random-effects model was selected because these studies are estimating effects that are related but not identical 28 ; studies use different designs, and examined different product types (as described above) across different years. The summary effect in the present study is therefore an estimate of the mean of the distribution of underlying effects. 29 The two-step DerSimonian and Laird estimator was selected over alternatives such as the original one-step DerSimonian and Laird estimator and the Paule-Mandel estimator because the latter have been shown to introduce bias. 30 As a sensitivity test, the one-step estimator were also implemented. Three separate models were implemented with these methods. The first analyzed the own-price elasticity of ENDS; the second the cross-price elasticity of ENDS with respect to cigarette price; the third the cross-price elasticity of cigarettes with respect to ENDS price. Where studies presented different effect estimates for different product types (e.g. one for disposable ENDS and another for reusable ENDS), both were included as separate effects in the same model, as they originate from different data. Some studies also provided both own-price and cross-price effects; each was used in the corresponding models above. Heterogeneity of effects was assessed with the Q statistic, tested for statistical significance as a chi-square score with degrees of freedom df = number of studies − 1 and alpha = 0.05 . The I 2 statistic and its CI was also calculated to reflect the overlap of individual studies’ CIs. 31 Finally, the T 2 statistic was calculated to provide a sample estimate of the standard deviation of underlying effects T = T 2 around the mean effect. Analyses were conducted in Python version 3.7.6 with the packages Numpy version 1.18.1, Pandas version 1.0.1, Matplotlib version 3.1.3, Scipy version 1.4.1, and Zepid version 0.9.0. Results Search results PubMed searches for the two search term combinations ‘e-cigarette’ + ‘own-price’ and ‘e-cigarette’ + ‘cross-price’ returned five and seven results respectively. Google Scholar searches for the same combinations returned 102 results and 252 results respectively. After reviewing these results for eligibility, 23 studies that assessed relevant elasticities were retained. All excluded articles did not assess relevant elasticities. Of the 23 studies retained, 10 did not use sales/purchases outcomes (e.g., they instead used prevalence/frequency or other outcomes). These 10 studies are summarized narratively because sales/purchases and prevalence/frequency/other outcomes are not appropriate for direct comparison, even in a random-effects model, and because each combination of outcome (current use, daily use) and population (adults, adolescents) had too few results for separate model-based meta-analyses. Of the remaining 13 studies considered appropriate for inclusion, nine reported both own-price and cross-price elasticities, two reported only own-price elasticities, and two reported only cross-price elasticities. Reporting of different elasticities for different product types from these studies provided 14 separate own-price elasticities and 15 separate cross-price elasticities for modelling. Of the 13 included studies, the majority were US-based, with the only exceptions being Stoklosa et al . 32 which studied the EU, and Grace et al . 33 which studied New Zealand. Of the 14 own-price estimates, three examined disposable ENDS, three examined reusable or rechargeable ENDS, one examined e-liquid, and the remaining studies examined multiple product types. Of the 15 cross-price estimates, three estimates examined disposable ENDS, three examined reusable or rechargeable ENDS, two examined e-liquid, and the remaining studies examined multiple product types. ENDS own-price elasticity All studies estimated a negative own-price elasticity, and none of the CIs crossed zero. The random-effects model summary effect for ENDS own-price elasticity was -1.10 (95% CI: -1.39 – -0.80). As a sensitivity test, the one-step DerSimonian and Laird estimator provides a summary effect of -1.12 (-1.46 – -0.78) which is not meaningfully different from the two-step result. The Q statistic for the own-price two-step model was 310.2 with 13 degrees of freedom, providing a p -value <0.001, which indicates statistically significant heterogeneity. The I 2 statistic was 95.8% (94.3%–96.9%), which is high 31 and is evidence that the underlying effects vary. Finally, the square root of the T 2 statistic provided a sample estimate of the standard deviation of underlying effects of 0.47 around the mean effect -1.10. To explore the heterogeneity of these studies, subgroup analyses were undertaken. A subgroup analysis of those studies which analyzed multiple product types and which used commercial retail/market-level models (n=6 studies) yielded a Q statistic of 4.2 with five degrees of freedom, providing a p -value of 0.52. This indicates homogeneity across these studies. For this subgroup, the summary effect was -1.15 (-1.34 – -0.97), which is statistically consistent with the whole-group analysis, and implies that a 10% increase in ENDS price is associated with an 11.5% (9.7%–13.4%) decrease in ENDS demand. This subgroup represents the largest subgroup with a non-significant Q-statistic, and consists of a sufficient number of studies for meta-analysis. 34 Figure 1 shows the forest plot for ENDS own-price elasticities from this homogeneous group of studies. Figure 1. Forest plot of own-price elasticity of ENDS. CI: confidence interval. Table 1 summarizes studies on ENDS own-elasticity which were excluded from the meta-analysis model because they used different outcome measures (e.g., prevalence) or non-comparable populations (e.g., adolescents or adult subpopulations). These studies all report negative own-elasticity of ENDS across product types and study models, consistent in direction and magnitude to the meta-analyzed studies in Figure 1 . Increased ENDS price is associated with decreased ENDS purchase, ENDS use prevalence, and ENDS use frequency among adults and adolescents in these studies. Table 1. Articles narratively reviewed. Article name, year Region & participants Outcome variable(s) Data sources Model ENDS type Result and interpretation Own elasticity of ENDS Pesko, Kenkel, Wang and Hughes 35 United States, adult smokers Likelihood of purchasing ENDS KnowledgePanel sample Hypothetical purchasing experiment Disposable Elasticity: -1.834 (-2.047– -1.621) (Evaluated at $6 baseline). A 10% increase in ENDS price above $6 was associated with an 18% decrease in ENDS selection. Reason for exclusion from meta-analysis model: different outcome measure. Shang, Weaver, White, Huang, Nonnemaker, Cheng and Chaloupka 36 United States, adult smokers who either used ENDS or were open to using ENDS Preference for ENDS selection KnowledgePanel sample Hypothetical purchasing experiment Refillable Mixed logit coefficient: -0.149 (-0.223– -0.0745). Higher ENDS price is associated with lower probability of choosing ENDS. Reason for exclusion from meta-analysis model: different outcome measure. Snider, Cummings and Bickel 37 United States, adult daily smokers (10+ cigarettes per day) Number of ENDS hypothetically purchased Amazon Mechanical Turk sample Hypothetical purchasing experiment Disposable Elasticity: -5.067 (-5.229– -4.928) among daily ENDS users. -4.699 (-4.891– -4.539) among monthly ENDS users. Reason for exclusion from meta-analysis model: non-generalizable subpopulation (daily smokers, daily ENDS users). Pesko, Courtemanche and Catherine Maclean 38 United States, adults Current (some days or every day) and daily ENDS use BRFSS, NHIS, CDC Fixed effects regression model E-liquid A $1.00 increase in tax per ml of e-liquid non-significantly decreases probability of current vaping by 15.3%, and daily vaping by 14.2%. Reason for exclusion from meta-analysis model: different outcome measure. Friedman and Pesko 39 United States, young adults (age 18–25) Recent (some days or every day) and daily ENDS use CPS-TUS Fixed effects regression model E-liquid A $1 increase in ENDS tax was associated with a significant 2.5 percentage point decrease in daily ENDS use, and a non-significant 2.6 percentage point decrease in recent ENDS use. NOTE: This study was published after literature searches concluded but was brought to the attention of the authors of the present study. Reason for exclusion from meta-analysis model: different outcome measure. Jin, Kenkel, Lovenheim, Mathios and Wang 40 United States, adults Past 30-day ENDS use NielsenIQ Custom Survey Fixed effects regression model Unknown Exposure to ENDS tax was associated with a non-significant decrease in number of days ENDS were used in the past 30-days of 0.352 days, and a non-significant 2.1 percentage point decrease in probability of ENDS use. NOTE: This study was published after literature searches concluded but was brought to the attention of the authors of the present study. Reason for exclusion from meta-analysis model: different outcome measure. Pesko, Huang, Johnston and Chaloupka 41 United States, adolescents Current (past 30-day) ENDS use and number of days ENDS were used in past 30-days Nielsen Retail Scanner, MTF Fixed effects regression model Disposable & refillable Elasticity: -0.649 (-1.431–0.133) for prevalence & disposables. -1.788 (-3.154– -0.421) for number of days & disposables. A 10% increase in disposable ENDS price was associated with a non-significant 6.5% decrease in overall ENDS use prevalence, and a significant 18% decrease in number of days ENDS were used in the past 30 days. -0.426 (-1.759–0.908) for prevalence & refillable. 0.549 (-1.621–2.720) for number of days & refillable. A 10% increase in refillable ENDS price was associated with a non-significant 4.3% decrease in overall ENDS use prevalence and a non-significant 5% increase in number of days used. Reason for exclusion from meta-analysis model: different outcome measure. Pesko and Warman 19 United States, adolescents Current (past 30-day) ENDS use and number of days ENDS were used in past 30-days Nielsen Retail Scanner, NYTS Fixed effects regression model Disposable & cartridge Elasticity: -0.666 (-2.789–1.457) for prevalence & disposables. 2.902 (-3.121–8.925) for number of days % disposables. A 10% increase in disposable ENDS price was associated with a non-significant 6.7% decrease in overall ENDS use prevalence and a non-significant 29% increase in number of days ENDS were used in the past 30 days. -2.236 (-3.855– -0.617) for prevalence & cartridges. -2.382 (-7.090–2.326) for number of days & cartridges. A 10% increase in ENDS cartridge price was associated with a significant 22% decrease in overall ENDS use prevalence and a non-significant 24% decrease in number of days used. Reason for exclusion from meta-analysis model: different outcome measure. Cantrell, Huang, Greenberg, Xiao, Hair and Vallone 42 United States, adolescents Current (past 30-day) ENDS use TLC Fixed effects regression model Rechargeable Elasticity: -0.06 (-0.134–0.014) A 10% increase in rechargeable ENDS price was associated with a non-significant 0.6% decrease in past 30-day ENDS use prevalence. Reason for exclusion from meta-analysis model: different outcome measure. Cross-price elasticity of ENDS with respect to cigarette price Snider, Cummings and Bickel 37 United States, adult daily smokers (10+ cigarettes per day) Number of ENDS hypothetically purchased Amazon Mechanical Turk sample Hypothetical purchasing experiment Disposable Positive cross-price elasticity of ENDS demand with respect to cigarette price, with steeper demand curves for less frequent ENDS users. Corresponding elasticities were not reported and could not be derived from this article’s figures. Reason for exclusion from meta-analysis model: non-generalizable subpopulation (daily smokers, daily ENDS users) and exact elasticities not reported. Cotti, Nesson and Tefft 43 United States, adults Probability of ENDS purchase Nielsen Consumer Panel, CDC STATE Fixed effects regression model Multiple A $1 increase in cigarette excise tax was associated with a non-significant -0.09 (-0.188–0.008) percentage point change in probability of ENDS purchase. Reason for exclusion from meta-analysis model: different outcome measure. Pesko, Courtemanche and Catherine Maclean 38 United States, adults Current (some days or every day) and daily ENDS use BRFSS, NHIS, CDC Fixed effects regression model E-liquid A $1.00 increase in cigarette excise tax results in a non-significant 7.4% increase in current (every day or some days) ENDS use, and a significant 14.2% increase in daily ENDS use. Reason for exclusion from meta-analysis model: different outcome measure. Friedman and Pesko 39 United States, young adults (age 18–25) Recent (some days or every day) and daily ENDS use CPS-TUS Fixed effects regression model E-liquid A $1 increase in cigarette tax was associated with a significant 2.1 percentage point increase in recent ENDS use, and a significant 2.5 percentage point increase in daily ENDS use. NOTE: This study was published after literature searches concluded but was brought to the attention of the authors of the present study. Reason for exclusion from meta-analysis model: different outcome measure. Jin, Kenkel, Lovenheim, Mathios and Wang 40 United States, adults Past 30-day ENDS use NielsenIQ Custom Survey Fixed effects regression model Unknown Exposure to cigarette tax was associated with a non-significant increase in number of days ENDS were used in the past 30-days of 0.281 days, and a non-significant 1.2 percentage point increase in probability of ENDS use. NOTE: This study was published after literature searches concluded but was brought to the attention of the authors of the present study. Reason for exclusion from meta-analysis model: different outcome measure. Pesko, Huang, Johnston and Chaloupka 41 United States, adolescents Current (past 30-day) ENDS use and number of days ENDS were used in past 30-days Nielsen Retail Scanner, MTF Fixed effects regression model Disposable & refillable Elasticity: -0.919 (-3.583–1.744) for prevalence & disposables. -0.258 (-3.570–3.055) for number of days % disposables. A 10% increase in cigarette price was associated with a non-significant 9.2% decrease in disposable ENDS use prevalence, and a non-significant 2.6% decrease in number of days disposable ENDS were used in the past 30 days. -1.287 (-3.808–1.235) for prevalence & refillable. -1.232 (-4.523–2.058) for number of days $ refillable. Similarly, a 10% increase in cigarette price was associated with a non-significant 12.9% decrease in refillable ENDS use prevalence and a non-significant 12.3% decrease in number of days used. Reason for exclusion from meta-analysis model: different outcome measure. Pesko and Warman 19 United States, adolescents Current (past 30-day) ENDS use and number of days ENDS were used in past 30-days Nielsen Retail Scanner, NYTS Fixed effects regression model Disposable & cartridge Elasticity: 3.526 (0.265–6.787) for prevalence. 14.26 (-12.395–40.915) for number of days used. A 10% increase in cigarette price was associated with a significant 35% increase in current (past 30-day) ENDS use prevalence and a non-significant 143% increase in number of days ENDS were used in the past 30 days. Reason for exclusion from meta-analysis model: different outcome measure. Cantrell, Huang, Greenberg, Xiao, Hair and Vallone 42 United States, adolescents Current (past 30-day) ENDS use TLC Regression model Rechargeable Elasticity: 0.94 (-0.15–2.03). A 10% increase in cigarette price was associated with a non-significant 9.4% increase in past 30-day rechargeable ENDS use prevalence among adolescents. Reason for exclusion from meta-analysis model: different outcome measure. Chan, Gartner, Lim, Sun, Hall, Connor, Stjepanović and Leung 44 International (47 countries), adolescents Current (past 30-day) ENDS use and frequent (20+ days out of past 30) ENDS use GYTS Regression model Multiple Compared to adolescents in countries where cigarette taxes comprise <25% of the price of cigarettes, adolescents in countries where cigarette taxes comprise ≥75% of the price of cigarettes had higher odds of current ENDS use (odds ratio=2.58; 99.58% CI, 1.28-5.21) and frequent ENDS use (odds ratio=6.18; 99.58% CI, 2.23-17.15). NOTE: This study was published after literature searches concluded but was brought to the attention of the authors of the present study. Reason for exclusion from meta-analysis model: different outcome measure. Cross-price elasticity of cigarettes with respect to ENDS price Pesko, Courtemanche and Catherine Maclean 38 United States, adults Daily smoking propensity BRFSS, NHIS, CDC Fixed effects regression model E-liquid A $1.00 increase in tax per ml of e-liquid results in a significant 5.3% increase in daily cigarette smoking propensity. Reason for exclusion from meta-analysis model: different outcome measure. Saffer, Dench, Grossman and Dave 45 United States, adults Current (every day or some days) cigarette smoking prevalence CPS-TUS Difference-in-differences model Multiple A 10% increase in ENDS price is associated with at least a 1.3% increase in current (every day or some days) cigarette smoking prevalence. Reason for exclusion from meta-analysis model: different outcome measure. Abouk, Adams, Feng, Maclean and Pesko 46 United States, pregnant adult women Prenatal smoking, number of cigarettes smoked per day NCHS, Vapor Products Tax Data Center, American Nonsmokers Rights Foundation, Tax Foundation Fixed effects regression model Multiple A $1.00 increase in ENDS tax significantly increases prenatal smoking by 5.8–7.7% and the number of cigarettes smoked per day by 8.9–10.5%. Reason for exclusion from meta-analysis model: non-generalizable subpopulation (pregnant women) and different outcome measure. Friedman and Pesko 39 United States, young adults (age 18–25) Daily and recent (every day or some days) cigarette smoking CPS-TUS Fixed effects regression model E-liquid A $1 increase in ENDS tax was associated with a significant 3.7 percentage point increase in recent smoking, and non-significant 2.5 percentage point increase in daily smoking. NOTE: This study was published after literature searches concluded but was brought to the attention of the authors of the present study. Reason for exclusion from meta-analysis model: different outcome measure. Pesko and Warman 19 United States, adolescents Current (past 30-day) cigarette smoking prevalence and number of cigarette smoked in past 30-days Nielsen Retail Scanner, NYTS Fixed effects regression model Disposable & cartridge Elasticity: 0.209 (-1.210–1.628) for prevalence & disposables. -0.412 (-3.268–2.444) for number of cigarettes & disposables. A 10% increase in disposable ENDS price was associated with a non-significant 2.1% increase in current (past 30-day) cigarette smoking prevalence and a non-significant 4.1% decrease in number of cigarettes smoked in the past 30 days. -0.151 (-1.686–1.384) for prevalence & cartridges. 2.090 (0.201–3.979) for number of cigarettes & cartridges. Also, a 10% increase in ENDS cartridge price was associated with a non-significant 1.5% decrease in cigarette smoking prevalence and a significant 21% increase in number of cigarettes smoked. Reason for exclusion from meta-analysis model: different outcome measure. Cantrell, Huang, Greenberg, Xiao, Hair and Vallone 42 United States, adolescents Current (past 30-day) cigarette smoking prevalence. TLC Regression model Rechargeable Elasticity: 0.01 (-0.00227–0.00223). A 10% increase in rechargeable ENDS price was associated with a non-significant 0.1% increase in past 30-day cigarette smoking prevalence. Reason for exclusion from meta-analysis model: different outcome measure. Mathios ( https://youtu.be/6K6dUA8KjOI ) United States, adults Probability of cigarette choice Own sample Hypothetical purchasing experiment Unknown A $1 increase in ENDS price was associated with a significant increase in immediate cigarette choice (linear choice probability for ENDS -0.018, p <0.01; and for cigarettes 0.017, p <0.01). NOTE: These findings are work-in-progress. This study was not identified through PubMed or Google Scholar but was brought to the attention of the authors of the present study. Reason for exclusion from meta-analysis model: unpublished work and different outcome measure. Cross-price elasticity of ENDS with respect to cigarette price All studies examined adults and estimated a positive cross-price elasticity, with the CIs of eight of the 14 estimates crossing zero. The random-effects model summary effect for ENDS cross-price elasticity with respect to cigarette price was 1.75 (0.92–2.58), with the CI not crossing zero. As a sensitivity test, the one-step DerSimonian and Laird estimator provides a summary effect of 1.80 (0.84–2.76) which is not meaningfully different from the two-step result. The Q statistic for the cross-price two-step model was approximately 130.7 with 13 degrees of freedom, providing a p -value <0.001, which indicates statistically significant heterogeneity. The I 2 statistic was 90.0% (85.1%–93.4%), which is high 31 and is evidence that the underlying effects vary. Finally, the square root of the T 2 statistic provided a sample estimate of the standard deviation of underlying effects of 1.18 around the mean effect 1.75. To explore the heterogeneity of these studies, subgroup analyses were undertaken. A subgroup analysis of those studies which used commercial retail/market-level models (n=11 studies) yielded a Q statistic of 8.0 with 10 degrees of freedom, providing a p -value of 0.63. This indicates homogeneity across these studies. For this subgroup, the summary effect was 0.98 (0.57 – 1.38), which is directionally and statistically consistent with, but half the magnitude of, the whole-group analysis result, and implies that a 10% increase in cigarette price is associated with a 9.8% (5.7%–13.8%) increase in ENDS demand. This subgroup represents the largest subgroup with non-significant Q-statistic. Figure 2 shows the forest plot for cross elasticity of ENDS with respect to cigarette price from this homogeneous group of studies. Figure 2. Forest plot of cross elasticity of ENDS with respect to cigarette price. CI: confidence interval. Table 1 summarizes studies which examined the cross-price elasticity of ENDS with respect to cigarette price. These were excluded from the meta-analysis model because they used different outcome measures (e.g., prevalence), non-comparable populations (e.g., adolescents or adult subpopulations), or because exact elasticities were not reported. Consistent with the meta-analysis in Figure 2 , Snider et al ., 37 Pesko et al ., 38 Pesko and Warman, 19 and Friedman and Pesko 39 suggest that higher cigarette price is associated with significantly increased number of ENDS purchased and increased ENDS use prevalence. Cotti et al . 43 and Pesko et al . 41 find negative cross-price elasticity of ENDS with respect to cigarettes, however these results did not reach statistical significance. Most recently, Chan et al ., 44 analyzing data from 47 countries participating in the World Health Organization’s Global Youth Tobacco Survey, found significant associations between higher cigarette taxes and higher prevalence of adolescent ENDS use. Cross-price elasticity of cigarettes with respect to ENDS price All studies examined adults. The random-effects model summary effect for cigarette cross-price elasticity with respect to ENDS price was 0.002 (-0.009–0.014), with the CI including zero. As a sensitivity test, the one-step DerSimonian and Laird estimator provides a summary effect of 0.002 (-0.003–0.007) which is practically identical to the two-step result. The Q statistic for the cross-price two-step model was approximately 15.1 with seven degrees of freedom, providing a p -value of 0.035, which indicates statistically significant heterogeneity. The I 2 statistic was 53.7% (0.0%–79.1%), which is moderate 31 and suggests approximately half of the observed variance represents real differences in effect size. Finally, the square root of the T 2 statistic provided a sample estimate of the standard deviation of underlying effects of 0.009 around the mean effect 0.002. To explore the heterogeneity of these studies, subgroup analyses were undertaken. Subgroup analyses by specific product types and study types did not resolve the heterogeneity. However, a subgroup analysis of those studies published after 2017 (i.e., the most recent studies most relevant to the current cigarette and ENDS markets; n=6 studies) yielded a Q statistic of 11.1 with five degrees of freedom, providing a p -value of 0.50. This indicates homogeneity across these studies. For this subgroup, the summary effect was 0.114 (-0.054 – 0.282), which is non-significant and positive. This subgroup represents the largest subgroup with non-significant Q-statistic. This implies that a 10% increase in ENDS price is non-significantly associated with a 1.1% (-0.5%–2.8%) increase in cigarette demand. Figure 3 shows the forest plot for cross elasticity of cigarettes with respect to ENDS price from this homogeneous group of studies. Figure 3. Forest plot of cross elasticity of cigarettes with respect to ENDS price. Effects based on commercial retail/market-level models are shown as circles. Effects based on hypothetical purchasing experiments are shown as squares. The summary effect is shown as a diamond. CI: confidence interval. Table 1 summarizes studies which examined the cross-price elasticity of cigarettes with respect to ENDS price. These were excluded from the meta-analysis model because they used different outcome measures (e.g., prevalence), non-comparable populations (e.g., adolescents or adult subpopulations), or because they contain unpublished findings. Pesko et al ., 38 Saffer et al ., 45 Abouk et al ., 46 and Friedman and Pesko 39 all find statistically significant positive cross-price elasticity, indicating that increased ENDS price is associated with increased cigarette smoking prevalence and propensity among adults. In as-yet unpublished work, Mathios reports that in hypothetical purchasing experiments, when faced with increased ENDS price, users immediately choose cigarettes rather than quitting ENDS ( https://youtu.be/6K6dUA8KjOI ). Among adolescents, Pesko and Warman 19 report a significant positive association between ENDS cartridge price and number of cigarettes smoked, while other outcomes in this study and in Cantrell et al . 42 did not reach statistical significance. Findings in this narrative summary are directionally consistent the meta-analysis in Figure 3 . Discussion The results of this review are consistent with a significant negative ENDS own-price elasticity; a 10% increase in ENDS price is associated with an 11.5% decrease in ENDS demand. Cross-price elasticity of ENDS with respect to cigarette price is significant and positive; a 10% increase in cigarette price is associated with a 9.8% increase in ENDS demand. This implies that ENDS are substitutes for cigarettes. A 10% increase in ENDS price is associated with a 1.1% increase in cigarette demand, but this result did not reach statistical significance in this model. All narratively summarized articles (e.g., those with prevalence outcomes) suggested a significant positive association between ENDS price and cigarette smoking prevalence and selection among adults, and to some extent among adolescents. Studies that could not be included in the meta-analysis generally are consistent with the meta-analysis for ENDS own-price elasticity, as well as cross-price elasticity. ENDS own-price elasticity is consistently negative in the prevalence/frequency/other outcome studies, which is unsurprising but validates the methods used in the present study. Similarly, most prevalence/frequency/other outcome studies of ENDS cross-price elasticity with respect to cigarette price report a positive (though not always significant) effect, indicating that higher cigarette prices are associated with higher ENDS use, suggesting product substitution. While the summary effect for the sales/purchases studies in the meta-analysis of cigarette elasticity with respect to ENDS price did not reach statistical significance, the prevalence/frequency/other outcomes studies (those not included in the meta-analysis) reported a consistent, albeit not always significant, increase in adult cigarette smoking in response to higher ENDS price, suggesting substitution. One reason for the non-significant summary effect in the meta-analyzed studies may be the very different sizes of the cigarette market versus the ENDS market: retail data show that tracked per-capita cigarette sales are approximately 10 times those of per-capita ENDS units. 25 The impact of a price change in the larger cigarette market on the smaller ENDS market may be more easily measurable, especially since most ENDS users have a history of smoking cigarettes ( https://cancercontrol.cancer.gov/brp/tcrb/tus-cps/results/2018-2019/table-3 ) and thus have a history of using one product as a substitute for the other. Conversely, the impact of a price change in the smaller ENDS market on the larger cigarette market may be more difficult to detect, especially given that the majority of smokers have never used ENDS. 47 This suggests that a more noticeable substitution effect would occur where ENDS uptake is higher, or among smokers who already have a history of ENDS use. Indeed, a larger decline in smoking prevalence attributable to ENDS has been shown in younger age groups, which have higher ENDS use prevalence. 16 , 48 Similarly, this explanation is also supported by the sales/purchases studies with a positive effect, 22 , 49 being from more recent years, when ENDS use was higher, compared to other studies done in earlier years when ENDS sales were significantly lower. 25 Further research is needed to examine these substitution effects among different subpopulations who differ by ENDS uptake or history, and the specific trajectory of product use. Other factors could also contribute to this phenomenon. The main finding of a price-driven substitution effect between cigarettes and ENDS is essential to consider for well-designed tobacco policy. In particular, ENDS regulations should be coordinated with cigarette regulations to incentivize nicotine users towards less harmful products. Policies that tax ENDS more heavily than cigarettes have the opposite incentive structure and are likely to exacerbate the tobacco-related health burden. 38 Because ENDS users are exposed to much lower levels of harmful constituents than are cigarette smokers, 1 , 2 if ENDS users are driven back toward cigarette smoking by disproportionate ENDS taxes, this has the potential for net public health harm. Important limitations should be considered when interpreting these findings. Other types of policies (e.g., minimum age of tobacco purchase, flavor bans) that would be expected to impact demand were not considered in the present study. The elasticity estimates analyzed here reflect the underlying limitations of the corresponding studies; for example, studies using retail data do not track online or specialty vape/tobacco store sales, introducing uncertainty into the estimates. The effects were drawn from studies across different product types and different years – over which the tobacco market changed substantially – as well as different methodological designs (e.g. real-world retail data versus purchasing task studies). While some of the analyses meta-analyzed regressed quantity against price to estimate a demand curve, others used taxes. While we argue that the high pass-through fraction makes prices and tax changes comparable, future meta-analyses should distinguish between prices and taxes as subgroups when sample size (number of studies) allows. Although the random-effects model used implicitly assumes the underlying effects are related but not identical, care should be taken when applying the summary effect to the entire ENDS product category across all years and populations. Due to the low number of studies, the meta-analysis is not broken out by price vs. tax changes, or by region. The meta-analytic statistics indicated considerable heterogeneity across studies, suggesting that other factors, whether methodological or substantive, may be important to understanding these elasticity effects, and further analyses will be needed to identify those. As previously noted, the majority of studies are from the US, and caution should be taken in generalizing to other geographies. Future reviews may include additional search terms and search engines. Despite these limitations, this study demonstrates a significant effect of ENDS cross-price elasticity with respect to cigarette price, indicating a robust substitution effect. The present study not only extends the findings of a prior systematic review and meta-analysis 24 using a substantial number of additional studies, but also for the first time presents an analysis of the cross-price elasticity of cigarettes with respect to ENDS price, and summarizes studies on sales and survey data. Our suggestion that asymmetric market sizes may account for the different-sized cross-price elasticities between two economic substitutes may be generalizable to other elasticity studies. The results of this systematic review and meta-analysis are consistent with a substitution effect between cigarettes and ENDS, such that price increases in cigarettes were associated with higher demand for ENDS. Evidence for an association between price increases in ENDS and higher demand for cigarettes has support in prevalence/frequency studies, but the effect did not reach statistical significance in a meta-analysis of sales/purchases studies, likely because the much smaller ENDS market is limited in its effects on the larger cigarette market. Further research is needed among populations with higher ENDS uptake (e.g., young adults) and/or smokers with a history of using ENDS. This economic substitution effect should be considered in tobacco policy – along with where each product falls on the risk continuum – so that cigarette and ENDS regulations are coordinated to disincentivize combustible tobacco use. Ethical considerations This study uses only publicly available de-identified aggregated data from previously published works. Under exemption four of NIH definitions, this research is therefore exempt from NIH human subjects research. Data availability Underlying data OSF: Supplemental materials for paper: Meta-Analysis of E-Cigarette Price Elasticity. https://doi.org/10.17605/OSF.IO/UFV48 . 50 This project contains the following underlying software and data: • Analytic code file 1: Statistical-Analysis-Code.ipynb • Data file 1: Data.xlsx Reporting guidelines PRISMA checklist and flowchart for ‘Meta-analysis of e-cigarette price elasticity’. https://doi.org/10.17605/OSF.IO/UFV48 . 50 Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0). Acknowledgements The authors would like to thank Dr Saul Shiffman and Joe Gitchell of PinneyAssociates, Inc. for reviewing a preliminary draft of this manuscript. References 1. 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Publisher Full Text Comments on this article Comments (0) Version 1 VERSION 1 PUBLISHED 02 Feb 2023 ADD YOUR COMMENT Comment Author details Author details 1 PinneyAssociates, Inc., Pittsburgh, Pennsylvania, USA Arielle Selya Roles: Conceptualization, Data Curation, Formal Analysis, Writing – Original Draft Preparation Floe Foxon Roles: Conceptualization, Data Curation, Formal Analysis, Methodology, Software, Visualization, Writing – Original Draft Preparation Siddharth Chandra Roles: Formal Analysis, Methodology, Supervision, Writing – Review & Editing Erin Nealer Roles: Data Curation, Project Administration, Supervision, Writing – Review & Editing Competing interests Through PinneyAssociates, Inc. all authors provide consulting services on tobacco harm reduction on an exclusive basis to Juul Labs, Inc. Funding for these analyses was provided by Juul Labs, Inc. Juul Labs, Inc. commented on a draft of the manuscript, but did not otherwise participate in study execution, data analysis, writing, or decision to publish. Grant information Funding for these analyses was provided by Juul Labs, Inc. Juul Labs, Inc. commented on a draft of the manuscript, but did not otherwise participate in study execution, data analysis, writing, or decision to publish. Article Versions (1) version 1 Published: 02 Feb 2023, 12:121 https://doi.org/10.12688/f1000research.129233.1 Copyright © 2023 Selya A et al . This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Download Export To Sciwheel Bibtex EndNote ProCite Ref. 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