Effective Policing

Abstract

Forensic applications of polygraph techniques rely primarily on the control or comparison question test (CQT). The author describes the CQT and its theoretical basis, and how it is used and evaluated by the polygraph professionals, and by scientists at arms length from the polygraph community. Because the CQT (a) has a weak theoretical foundation, making it unlikely that it can be as accurate as polygraph proponents claim, (b) is biased against the innocent, and (c) may be subject to countermeasures used by the guilty to appear truthful, CQT results cannot constitute evidence of either deception or truthfulness. In the absence of insight into brain mechanisms that underlie deception, it may be difficult to develop a valid lie detector. However, methods are available for detecting guilty knowledge, information that only the perpetrator of a crime and the police possess, which are ripe for further development as forensic applications.