Facilitating Falsification: Devil's Advocacy in Dutch Police Investigations

Confirmation bias has been identified as a recurrent cause of wrongful convictions. To mitigate the risk of this bias, police investigators should devote effort to exploring and attempting to falsify alternative hypotheses about a crime. In the Netherlands, investigators in complex serious crime investigations are instructed to apply devil's advocacy (DA) to increase discussion and testing of alternative investigative theories. This study provides a first quantitative examination of whether DA is associated with more falsification-focused reasoning about evidence. Police investigators who regularly work with DA (n = 63), investigators who do not (n = 76), and laypersons (n = 88) read a fictional investigation report and judged the likelihood that the prime suspect was guilty both before and after asking follow-up questions and receiving additional information. None of the groups clearly demonstrated confirmation bias. Contrary to prediction, both investigator groups provided lower guilt-likelihood estimates than laypersons throughout, but DA-experienced and non-DA-experienced investigators did not differ significantly from one another on any outcome. DA experience was not associated with greater falsification-focused questioning, stronger weighting of exonerating evidence, or larger reductions in guilt-likelihood estimates. Exploratory analyses suggested that DA-experienced investigators asked fewer confirmatory questions than both other groups. Implications for future research and practice are discussed.