Investigator bias: Contextual influences on the assessment of criminal evidence

Abstract: DEGREE OF lICENTIATE IN PSYCHOLOGY, 2011 Abstract Rebelius, A. (2011). Investigator bias: Contextual influences on the assessment of criminal evidence. Department of Psychology, University of Gothenburg, Sweden The success of a criminal investigation depends to a great extent on the investigator's ability to make correct decisions based on evaluations of available information and evidence. Ideally, such evaluations should not be influenced by contextual factors, such as preconceptions, time pressure or occupational norms, but on the properties of the evidence itself. However, the results of recent research challenge this ideal, suggesting instead that evidence evaluation is rather sensitive to contextual influence (Ask & Granhag, 2007a, 2007b; Dror, Charlton, & Peron, 2006). Applying theoretical frarneworks developed in social and cognitive psychology, the present thesis examines the effects of contextual influence on criminal investigators' judgments. The aim of Study I was to test the hypothesis that exposure to occupational norms can activate distinct informationprocessing goais. Experienced police investigators (N := 104) participated in the study. Af ter having read normative descriptions intended to activate goals related to information processing (i.e. efficiency or thoroughness), the investigators were presented with a criminal case description. Concluding the case description was a witness statement designed to be either congruent (i.e. incriminating) or incongruent (Le. exculpatory) with the other information in the case. In line with expectations, exposure to norms associated with efficiency (vs. thoroughness) sped up and reduced the depth of investigators' processing of the criminal evidence. In tum, the reduced depth of processing led to a decreased openness to the witness evidence presented at a late stage of the investigation. In addition, the goal activation opemted outside the investigators' awareness, illustrating the insidious cognitive influence of occupational norms. The focus of Study II was to examine investigators' perceptions of the reliability of incriminating and exonemting evidence of different types. Police trainees (N:= 117) in the role of investigators read the background of a homicide case and then received a piece of evidence that either confirmed or disconfirmed their prior suspicion against the suspect. Despite identical objective characteristics of the evidence, participants rated the disconfirming (vs. confirming) evidence as less reliable, and generated more arguments to question its reliability. This asymmetrical scepticism was stronger for participants judging witness evidence, compared to DNA and photo evidence, supporting the hypothesis that different types of evidence vary in 'elasticity' -the extent to which subjective interpretations can be justified. Interestingly, the observed effects were not limited to the specific evidence in the case, but also affected perceptions of the type of evidence in general, suggesting that reliability criteria for witness information are highly malleable and sensitive to contextual influence. Taken together, the findings from Study I and Study II suggests that the social and informational context exerts a major influence on information processing in criminal investigations. Keywords: Criminal investigation, Decision making, Contextual influence, Cognitive bias, Investigative psychology, Occupational norms, Evidence, Police ISSN 1101-718X GUIPSYKI A VH--247-SE Anna Rebelius, Department of Psychology, University of Gothenburg, P.O. Box 500, 40530 Gothenburg, Sweden. Phone: +46 (0)317861935, E-mail: [email protected]. Home page: www.clip.org.gu.se