Polygraph Examiner Awareness of Crime-Relevant Information and the Guilty Knowledge Test (original) (raw)
Related papers
Journal of Applied Psychology, 1999
This study focused on the Guilty Knowledge Test (GKT) -a psychophysiological detection method based on a series of multiple-choice questions, each having one relevant and several neutral (control) alternatives. The study examined a new method, designed to reduce false-positive outcomes, due to leakage of relevant items to innocent suspects, by introducing target items (i.e. items known to all examinees, but unrelated to the crime), to which subjects have to respond (e.g., by pressing a key), while answering the GKT questions. Informed innocents showed relatively larger electrodermal responses to the critical items than uninformed participants, but not as large as the responses made by guilty participants. No differences between informed and uninformed innocents were obtained with a respiration measure. The use of the target items tended to reduce the differences between informed and uninformed innocents. The results further demonstrated that electrodermal responding to the relevant items was correlated with memory of these items.
Estimating the Validity of the Guilty Knowledge Test
This experiment was designed to examine the external validity of the standard mock-crime procedure used extensively to evaluate the validity of polygraph tests. The authors manipulated the type of mock-crime procedure (standard vs. a more realistic version) and the time of test (immediate vs. delayed) and examined their effects on the validity of the Guilty Knowledge Test (GKT) and the recall rate of the relevant items. The results indicated that only the type of mock-crime affected the 2 outcome variables. The realistic procedure was associated with a lower recall rate and weaker detection efficiency than the standard procedure. However, these effects were mediated by the type of GKT questions used. Practical implications of these results are discussed.
Detection measures in real-life criminal guilty knowledge tests
Journal of Applied Psychology, 1992
The present study provides a first attempt to compare the validity of the respiration line length (RLL) and skin resistance response (SRR) amplitude in real-life criminal guilty knowledge tests (GKTs). GKT records of 40 innocent and 40 guilty Ss, for whom actual truth was established by confession, were assessed for their accuracy. When a predefined decision rule was used and inconclusive decisions were excluded, 97.4% of the innocent Ss and 53.3% of the guilty Ss were correctly classified with the SRR measure. For the RLL measure, the respective results were 97.2% and 53.1%. The combination of both measures improved detection of guilty Ss to 75.8% and decreased detection of innocent Ss to 94.1%. The combined measure seems to be a more useful means of identifying guilty suspects than each physiological measure alone. The results elaborate and extend those obtained in a previous field study conducted by Elaad (1990). We would like to thank Gershon Ben-Shakhar, Murray Kleiner, and three anonymous reviewers for their helpful comments.
Salience of guilty knowledge test items affects accuracy in realistic mock crimes
International Journal of Psychophysiology, 2006
Guilty Knowledge Test measuring electrodermal reactions was carried out in order to investigate the quality of different questions and the validity of the test in a situation that resembled a true crime. Fifty participants were randomly assigned to commit one of two realistic mock crimes, and were later tested with GKTs concerning both the crime they had enacted and the one they had no knowledge of. Different scoring systems (SCRs and peak amplitudes as well as raw and standardised scores) were employed and compared when analyzing the results. Although there were some false positives, the test was able to differentiate between the groups of guilty and innocent participants. With the best scoring systems, the test was able to classify up to 84% of the innocent and up to 76% of the guilty correctly according to a logistic regression analysis. ROC areas reflecting these same results reached values above .80. Questions on matters that demanded the participants' attention and were easier to remember had better discriminative power. With nearly all scoring methods, there was a significant interaction between the salience of the relevant items and the guilt of the participants. Participants reacted more strongly to salient relevant items when they were guilty, while no different reactions were observed for the non-salient items between guilty and innocent participants. It is suggested that, although the Guilty Knowledge Test appears to be a valid measure of guilty knowledge even in crimes that are close to real crimes, the principles on which guilty knowledge test questions are constructed should be more clearly specified.
International Journal of Psychophysiology, 2010
The accuracy of the Concealed Information Test (CIT) in detecting information concealed by informed innocent participants was assessed under varying levels of probability that the obtained information is related to the crime and is therefore correct. For this purpose, 64 participants were randomly assigned to four experimental conditions that were formed by probability levels that the gathered information is correct and is related to the crime. Either absolutely correct (100% correct), highly correct (80%, correct), highly incorrect (20% correct) or totally incorrect (0%, correct) conditions were created. Response generalization was manipulated by replacing 3 of 6 correct items with related stimuli. The replaced stimuli were related to the correct items either semantically, phonetically, or numerically. Informed innocent participants showed larger electrodermal responses to items with a higher probability of being correct. It was further found that participants elicited stronger responses to correct than to replaced items. Theoretical and practical implications of the present results are discussed.