A comparison of field and laboratory polygraphs in the detection of deception

This study compared the effectiveness of field and laboratory polygraphs in discriminating guilty and innocent subjects tested using the Control Question Technique (CQT). Subjects were 48 prisoners examined regarding a mock theft in a peer threat context; physiological responses were recorded simultaneously on a Lafayette field polygraph and a Sensor Medics laboratory polygraph. Overall hit rates were essentially the same whether classifications were based on quantitative measures from the laboratory polygraph or on numerical scores from the field polygraph (i.e., 73% and 79%, respectively), and in both cases the best discriminating measures were electrodermal activity and indices of respiration suppression. Further analyses revealed that errors of classification were mostly due to the failure of the available measures to differentiate between relevant and control questions for innocent subjects. These results indicate that the CQT is susceptible to false positive errors when subjects are tested under field-like circumstances, a problem that is not likely to be eliminated by refinements in instrumentation and scoring.