Suspects, Lies, and Videotape: An Analysis of Authentic High-Stake Liars - Mann, S., Vrij, A. and Bull, R. (2002)


Are there certain behaviors that differentiate a liar from a truth teller?
Determine if cognitive load increases lie behaviors.


Police video tapes from 16 suspect. 13 males, 3 females. 4 children (13,13,13 &15) and 12 adults (younger than 65). 15 Caucasian, 1 Asian.
Most participants had previously been known previously to the police.
Most crimes committed were theft, arson, attempted rape and murder.

Research Method

This was a quasi experiment. Quasi experiment: independent variable was not directly manipulated by the experimenter.


Two observers were asked to "Code data", weren't told much about the experiment previously. For every behavior of the participants it was coded with 1 truth telling score and one lie telling score. Some of the behaviors recorded:

1. Gaze Aversion
2. Blinking
3. Head movements
4. Speech disturbances (stuttering)
5. Pausing between words, and or sentences.
6. Hand and arm movements
7. Self manipulations
8. Hand/finger movements

Observers, not the suspects, were instructed to code the one hour video footage, also called content analysis. This is where they were asked to analyze and record quantitative, numerical data to remove subjectivity and increase detection of trends . They were not told the hypothesis or the nature of the clips, to enhance ignorance and deception. Once they coded the behaviors, they transformed into a manageable format so that the truths and the lies could easily be compared. The result was one truth-telling score and one lie telling score for each behavior of each participant.
Then, two observers were asked to independently code the behavior. After all of this collection of data, a Pearson correlation statistical test was used between the two independent observers and the others, which showed a strong consistency between the two codes. This means that there was no significant difference between the two coders.


  • Behaviors were not significantly different.

  • Noticeable differences were found between the hand, arm movements and pauses.

  • Gave some support to the cognitive load process. Behaviors leading to cognitive load would be blinking and pausing.

  • Weaknesses

  • Conclusions are speculative.

  • Small participant group.

  • Possible (slight) gender/ age bias

  • Ecological Validity

  • High level of ecological validity.
  • Explanations

  • Because it only looks for the causes of our behaviour in our thought processes, the cognitive approach is reductionist. It ignores possible causes for our behaviour that could have come from, for example, our social environment or our biology.

  • Strengths

  • High levels of control

  • Participants had no idea they were participating in a study (mainly because they were old tapes)

  • Ethics

    This study was ethical considering that everyone knew what was going on, they knew that they were in a study. Also they weren’t asked to do anything that would negatively affect them or anyone else. They study was pretty ethical.

    Mann, S., Vrij, A. and Bull, R. (2002)

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