The Usability and Effectiveness of the Finnish Investigative Instrument of Child Sexual Abuse in Mock Evaluations

The Finnish Investigative Instrument of Child Sexual Abuse (FICSA) is a computerized tool that uses Bayesian statistics to provide a base rate for an alleged child sexual abuse (CSA), using population-level information about correlates of CSA. FICSA can, thus, assist decision-making in investigations of CSA. Here, we compared forensic experts’ and students’ ability to use FICSA and whether its use affected the estimates of the probability of CSA in mock-scenarios. The use of FICSA was compared to only having access to the empirical information about CSA risk and protective factors, which FICSA is based on, and to unassisted decision-making. The 54 participants analyzed two scenarios of possible CSA and estimated the probability of the CSA allegation being true. The results show that participants using FICSA were prone to make technical mistakes that affect the correctness of the probability estimation. The performance of experts and students was equivalent in all the conditions, with the exception of the group using FICSA, where experts tended to deviate from the probability provided by FICSA more than students. Having only access to empirical information did not improve estimates compared to unassisted decision-making. Both students and experts tended to adjust the estimates provided by FICSA downwards, that is, to decrease the probability of abuse. We conclude that FICSA has the potential to assist investigators to correctly integrate evidence and calculate probabilities but that proper training is required.