Initial evidence for the assimilation hypothesis

ABSTRACT

The assimilation hypothesis dictates that knowledge of prior evidence makes legal decision makers assign more weight to subsequent evidence. For example, the evidentiary power of a line-up identification is perceived to be stronger if the decision maker knows that the suspect has confessed, compared to when knowledge of the confession is absent. In three studies, the assimilation hypothesis was tested. As expected, knowledge of DNA-evidence inflated the estimated strength of subsequent eyewitness identification evidence (Study 1), and also inflated overall conviction and conviction rate (Study 2). A similar assimilation effect was found with knowledge of the suspect’s dangerous psychopathology (i.e. psychopathic and anti-social personality traits). Such knowledge inflated the estimated strength of fingerprint evidence. In conclusion, the assimilation effect is a threat to rational legal decision making in both lays (Study 2) and professional judges (Studies 1 and 3).

KEYWORDS:

• Assimilation
• evidence
• cross-over-effect
• coherence-based reasoning
• CSI-effect

Disclosure statement

No potential conflict of interest was reported by the author.