The assessment and detection of deceit

When criminal justice investigators (police officers, lawyers, prosecutors, judges, juries, and so on) assess statements made by suspects, victims and witnesses, they are almost always confronted with an age old dilemma: how to distinguish between those who are telling the truth and those who are not. One way to examine this is by observing people's behaviour and analysing their speech content. This chapter reviews research findings on (i) differences in behaviour and speech content between liars and truth tellers, and (ii) people's ability to detect deceit while observing someone's behaviour and analysing someone's speech. The first part of this chapter addresses the relationship between behaviour and deception. This part will demonstrate that, although no single pattern of behaviour is uniquely related to deception (Pinocchio's nose does not exist), some behaviours are more likely to occur during deception than others. Also, it shows that people are generally not very good at detecting deceit when paying attention to someone's behaviour. Several reasons to explain this poor lie detection ability and some ideas how to improve behavioural lie detection will be discussed. The second part considers the relationship between speech content and deception. Although analyses of non-verbal behaviour are never formally used as evidence in criminal courts, verbal assessments sometimes are. This part of the chapter discusses the most popular verbal detection technique used in court to date: Statement Validity Assessment (SVA). Research has shown that some of the speech content criteria that SVA experts examine do differentiate between liars and truth tellers. Also, we will see that experts who employ this technique are able to detect lies and truths above the level of chance. However, their lie detection skills fall short to the level required for using their assessments as reliable evidence in criminal courts. Some limitations of SVA and ideas how to improve speech content lie detection will be discussed. Throughout this chapter methodological problems in deception research will be addressed. These are important as they raise questions about the generalisability of the research findings to legal settings. I will conclude with discussing some implications of the research findings for lie detection in legal settings.