The Impossibility of Expecting the Unexpected: Identity, Exchange, and a General Model of Transferred Expectations in Forensic Evidence Handling

Abstract

Expectancy effects in evidence handling pose a serious threat to the validity of analyses conducted by forensic examiners. This critical compromise creates an impasse regarding key assumptions of law regarding the admissibility of scientific evidence and testimony. The history of rules of law governing the use of scientific evidence are detailed, followed by a review of experimenter effects, observer effects, and a model that integrates them into a general theory of transferred expectations. Social exchange and identity are explored as factors that contribute to the existence of expectancy effects and their transfer. The general model posits that expectancy effects are communicated from observer to target (experimenter effect), and then are manifested between target and object (observer effect), when the analysis of an object impacts both the target and the original observer. Related subtopics of role theory, and conformity, norms, and deviance, further explain the maintenance of expectancy effects.

Keywords: forensic, expectancy effects, expectancy transfer, evidence handling