The utility and accuracy of post-conviction polygraph testing with sex offenders

PhD ThesisThe aims of the present research were two-fold: firstly, to investigate the utility of post-conviction polygraphy with community-based sex offenders; and secondly, to examine the accuracy of the polygraph in this context. The initial study examined whether periodic polygraph testing acted as a deterrent for engaging in risk behaviour. Fifty adult male sex offenders taking part in community treatment programs were allocated into 2 groups: "Polygraph Aware" subjects were told they would receive a polygraph examination in 3 months regarding their high-risk behaviours, while "Polygraph Unaware" subjects were told their behaviour would be reviewed in 3 months. Relevant behaviours for each subject were established at baseline interviews, following which both groups were polygraphed at 3 months. All subjects were polygraphed again at 6 months. Thirty-two subjects (64%) attended the first polygraph examination, with 31 (97%) disclosing an average of 2.45 high-risk behaviours each previously unknown to supervising probation officers. There was no significant difference between the two groups. Twenty-one subjects (42%) completed the second polygraph test, with 71% disclosing an average of 1.57 behaviours, a significant decrease compared with the first test. Disclosures to treatment providers and probation officers also increased. Polygraph testing resulted in offenders engaging in less high-risk behaviour, although the possibility that offenders fabricated reports of high-risk behaviours to satisfy examiners is also considered; similarly offenders seemed to be more honest with their supervisors, but this only occurred after the experience of the test itself. The second study examined the accuracy of the polygraph as used in a postconviction context with sex offenders. One hundred and seventy-six sex offenders engaged in treatment and required to complete biannual polygraph tests focussed upon offending and other risk behaviours. The participant's regular polygraph maintenance test was used for the study, however, in addition to the regular issues covered in this test the examiner included `drug use' over the preceding three months as a relevant question. Immediately after the polygraph test a hair specimen was collected and subsequently analysed for drugs. The polygraph was reasonably accurate with identifying truth telling (79%), while 21% were wrongly accused of drug use. Only a small number of offenders (n = 5) were found to be taking drugs and lying about having done so. The blind scorers correctly identified all of these individuals (100%). The Area under the curve index was . 88. The inter-rater reliability between the blind scorers and the original examiners was poor. The original examiners were less accurate than the blind scorers (Area under the curve index = . 68) and only correctly identified two of the five liars (40%). False positives were associated with lower intelligence and having experienced a sanction due to a polygraph result. False negatives were not associated with demographic characteristics, personality variables or intelligence. The majority of offenders found the polygraph to be helpful in both treatment and supervision. Nine per cent of offenders claimed to have made false disclosures; these individuals -had higher scores on ratings of Neuroticism and lower scores on ratings of Conscientiousness. The implications of these results are discussed. Overall, the findings support the view that the polygraph is both useful and accurate in the treatment and supervision of sex offenders