No safety in numbers
: detecting deception using a collective interviewing approach

Student thesis: Doctoral Thesis


Group interviewing, the topic of investigation in this thesis, has been neglected within the deception detection literature. Chapter 1 introduces the topic, and emphasises the importance of studying collective interviewing (whereby pairs are interviewed simultaneously) in a deception context. Chapter 2 explores the nature of deceit occurring within pairs in a police-style interview setting. Truth-telling pairs had lunch together, whilst lying pairs committed a mock crime. All pairs then had to convince an interviewer they were having lunch together. The interview protocol involved repeated questioning, but no significant differences were found between truth-telling pairs and lying pairs in terms of repetitions, omission errors, commission errors, contradictions, and dominance. The lack of significant findings are discussed with regards to the interview protocol employed. Chapter 3 describes two experiments. The first used an immigration-style interview context, and imposed cognitive load by implementing a forced turn-taking technique. Truth-telling pairs were real couples, whereas lying pairs were friends. All pairs were required to convince an interviewer they were a bona fide couple. Results showed that when forced to turn-take, truth-telling pairs continued on from one another, whereas lying pairs waited and repeated previously said information before continuing. The second experiment, a lie detection study, revealed that the three turn-taking cues improved people’s ability to accurately detect deceit. Chapter 4 is based on the first experiment mentioned in Chapter 3, but applies transactive memory theory to explore whether signs of truthfulness emerge through joint recall. Results showed that truth-telling pairs posed questions and provided cues to one another, handed over remembering responsibility, and finished each other’s sentences more than lying pairs. Chapter 5 discusses a study which applied the verifiability approach to alibi witness scenarios. Truth-telling pairs completed a mission together, whereas lying pairs were separated so that one completed the mission whilst the other committed a mock crime. All pairs then had to convince an investigator, first individually then collectively, that they completed the mission together. Results revealed that truth-telling pairs provided more checkable details demonstrating they were together, whereas lying pairs provided more uncheckable details. Additionally, the collective statements prompted only the truth-telling pairs to provide more checkable details demonstrating they were together. A comparison of the individual and collective statements for memory consistency and distortion showed that liars repeated more uncheckable details whilst truth-tellers omitted and committed more checkable details. Chapter 6 summarises the main findings obtained in this thesis, discusses the theoretical and practical implications, and suggests ideas for future research.
Date of Award27 Jan 2015
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorAldert Vrij (Supervisor), Sharon Leal (Supervisor) & Sam Mann (Supervisor)

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