An Examination of the Validity of the Concealed Information Test

  • Anita Fumagalli

Student thesis: Doctoral Thesis


This study investigates the validity of the Concealed Information Test (CIT), considered as the most accurate polygraph test able to discriminate guilty from innocent suspects (e.g. Ekman & O'Sullivan, 1991; Bull et al., 2004; Grubin & Madsen, 2005). Despite scientific support for the use of the CIT, the test is currently rarely employed, due to the lack of demonstration for its applicability within real forensic contexts (Kraphol, 2011). This thesis aims to provide further evidence of the CIT mechanisms and demonstrate new potential applicability as an investigative and preventative tool. This study addresses these aims by evaluating certain aspects of the validity of the CIT which have received less attention in literature: the effect of visual stimulation, the ability to detect criminal intentions and the application of the CIT in a group setting.

In order to conduct the analysis, the study recorded and analysed different physiological measurements: EDA (electrodermal activity), breathing and heart rate. Analyses were conducted to determine the accuracy of the test and the effects of the stimulations designed. Study I explored the basic mechanisms of the CIT and the impact of relevant information on participants’ physiological responses. For this purpose, the study used a standard CIT examination, which involves only verbal stimulation. Results from this study demonstrated the efficacy of the standard procedure of the CIT. In fact, the test was able to detect relevant information from guilty participants (SCR M=2.85; RLL M= -1.41; Cardio M= -0.5) and identify correctly innocent participants (SCR M=0.03; RLL M= 0.02; Cardio M= -0.07), showing a significant difference between the two groups (d=3.03; p=
In order to demonstrate the applicability of the CIT in forensic settings, Study II investigated the effectiveness of an alternative stimulation method: visual stimulation. Despite the amount of photographic evidence available in forensic cases, not many researchers have explored the potential of visually stimulating examinees during a polygraph examination. Results suggested that visual stimulation could increase the accuracy rates of the test. Specifically, the combination of verbal and visual stimulation had a stronger impact on participants’ physiological responses when compared with Study I. Results also presented a significant difference (d=2.05; p=
With the aim of suggesting a new applicability of the CIT in forensic settings, Study III evaluated the effectiveness of the CIT in a more realistic setting by attempting to detect
intentions to commit a crime. There is a lack of research around the potential applications of the CIT as a tool for preventing crimes, especially regarding suspect prioritization or planning prevention prior to a crime being committed. For this reason, Study III investigated the accuracy of the CIT when trying to detect criminal intentions after having planned a crime. Results from this study showed that the CIT was able to detect crime-related information from the experimental group (SCR M=7.39; RLL M= -1.41; Cardio M= -2.43), reporting a significant difference in the detection rate (d=7.35; p=
Finally, Study IV retained the methodological elements of Study III, but applied them within a group setting. Previous literature on deception (e.g. Granhag et al., 2015) exclusively focused on solo offenders. Therefore, there is a need to expand the research and develop new technologies for the prevention of groups of criminals as well. The purpose of this study was to examine whether crime-related information and intentions to commit a crime could be detected from a group of mock suspects. The results showed that the CIT was able to detect crime-related information from the mock suspects (SCR M=1.15; RLL M= -0.73; Cardio M= -0.1) with a significant difference (d=11.72; p=
A combination of SCR (Skin Conductance Response) scores, RLLs (Respiration Line Length) and heart rate was used for the analysis. Collective results from the studies concluded that the physiological measure with the highest detection rate was the SCR, compared to heart rate and RLL. This supports the current literature, which suggests that SCR is the most robust and accurate physiological measure to be used with the CIT (e.g. Bradley et al., 2011; Council, 2003b; Holden, 2000). However, conclusive arguments from the thesis took into account the combination of the three measures together, which generated larger validity rates for the test compared to the best scores from any single physiological measure.

Various factors limited the full accuracy rate of the test, causing the occurrence of false positive and false negative rates. Although some of the results were not optimal, this study provides a deeper understanding of the CIT mechanisms and proposes new potential applications. In conclusion, this study proposes the use of the CIT as a preventative tool within forensic settings; however, more research is required around the accuracy of the CIT in real settings, especially if applied to groups of examinees. With the benefit of future research, the CIT could support police investigations by detecting criminal information, prioritising and identifying potential suspects involved in solo or group criminal activities.
Date of Award2023
Original languageEnglish
SupervisorMaria Ioannou (Co-Supervisor) & John Synnott (Co-Supervisor)

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