Date of Award







Kristen Beyer


Confirmation bias occurs when a person believes in or searches for evidence to support his or her favored theory while ignoring or excusing disconfirmatory evidence and is disinclined to change his or her belief once he or she arrives at a conclusion. The purpose of this quantitative study was to examine whether emotionally charged evidence and evidence presentation order could influence an investigator's belief in a suspect's guilt. The study included 166 sworn police officers (basic training recruits, patrol officers, and criminal investigators) who completed online surveys in response to criminal vignettes across different scenarios to record their measure of guilt belief. Analysis of variance was used to assess the relationship between the 3 independent variables: duty assignment (recruit, patrol, investigator), scenario condition (child and adult sexual assault), and evidence presentation order (sequential, simultaneous, reverse sequential). The dependent variable was confirmation bias (Likert-scaled 0–10 guilt judgment). According to the study results, confirmation bias was least evident in criminal investigators with more experience and training, and both emotion and evidence presentation order can influence guilt judgment. The findings generalize to criminal investigators and attest to the importance of working to include and exclude suspects and to withhold judgment until all available evidence is analyzed. Investigators benefit from this study and through their improved decision making, society benefits as well. This study will contribute to the need for professional dialogue concerning objective fact finding by criminal investigators and avoiding incidents of wrongful conviction.