The Magic or Myth of Expertise: A Comparison of Judgment Processes between Forensic Experts and Lay Persons Based on Psychiatric Case Vignettes

Abstract

As a continuation of a previous study (Grøndahl, Grønnerød, & Sexton, 2009), we examined how 120 laypersons and 35 forensic experts (14 psychiatrists and 21 psychologists) differed in their judgment processes of forensic case vignettes. The vignettes contained descriptions of three components, namely social history, psychiatric history and criminal offense. We found important differences in how the groups used information when they rated insanity, risk and need for treatment. The professional groups emphasized all three case components as opposed to laypersons. As for priming, all the groups rated lower on risk and need for treatment when the case started with a positive description. More professional experience was related to lower insanity and treatment ratings and higher risk ratings. The professionals generally rated less confidence in their judgments compared to the laypersons. Professionals and lay persons thus seem to evaluate forensic material differently.

Key words:

• decision theory
• expertise
• forensic psychiatry
• law
• quality