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Abstract

In recent years, the need for enhanced methods of credibility assessment in criminal cases has become illuminated. Especially in cases of sexual assault, the words of the accused and complainant are often the sole evidence available to police. Consequently, researchers and practitioners have been searching for ways of differentiating truthful and deceptive accounts, focussing mainly on witnesses and victims. With its recent history, however, assessment based on verbal clues has been somewhat myopic and not well grounded in theory or integration. This thesis examined a general hypothesis, based upon conceptual information from a variety of perspectives, that reliable verbal indicators of deception exist in the interrogation situation. Sixty undergraduates were recruited for participation in research addressing “security effectiveness.” Participants either committed a theft “to test the effectiveness of a new security guard” or carried out a similar but innocuous task. They were then asked to provide either: (1)a truthful alibi (2)a partially deceptive account (3)a completely false alibi or (4)a truthful confession regarding the theft to “an interviewer also hired for the purpose of investigating thefts.” To increase motivation in the interview, honest and dishonest participants were offered a monetary incentive for convincing the interrogator of their veracity. The accounts were then transcribed and examined for the presence of eighteen language variables. A multivariate analysis of variance (MANOVA) revealed a profile of three variables which significantly differentiated the truthful and deceptive accounts (amount of detail reported, coherence of the account, and admissions of lack of memory). For example, dishonest participants provided much less detail (although not fewer words) in relating an event than truthful participants describing a similar event. Implications for credibility assessment in forensic interrogations are discussed, emphasizing the need for establishing external validity with eclectic research strategies.