Mann et Al (2002) Suspect, Lies, and Videotapes

/ alevelpsychologycie

AIMS:

To investigate the lying behaviour of suspects in police custody – a high-stake situation that is real life so would generate real lying.

PROCEDURE

  • Two observers coded the eight behaviours.
  • Not aware of which clips showed lies or truths
  • Not told aims or hypotheses
  • 1st observer = coded every clip
  • 2nd observers = coded random sample of 36 clips covering all suspects – inter-rate reliability could be measured.

Independent variable = suspects telling the truth or lie.

Dependent variable = the behaviour shows when telling a truth or a lie

Design:

  • Detectives at Kent Constabulary – asked to recollect tapes where the suspects had lied but also said the truth.
  • Researchers looked through the tapes to make sure that it was easy to corroborate the lie and truth.
  • An hour-long video -16 suspects.
  • The truths had to be comparable to the lies for inclusion.
  • 65 clips – 27 truths and 38 lies.
  • Length – 41.4 seconds to 368.4 (time has little effect on behaviour of the teller)

Content analysis:

  • Gaze aversion = looking away from interviewer
  • Blinking
  • Head movements
  • Self-manipulations
  • Illustrators = arm and hand movements
  • Hand/finger movements
  • Speech disturbances
  • Pauses = suspect stopped for more than 0.5 seconds in flowing conversation.

Behaviours were changed into a format, so that truths and lies could be directly compared.

Participants:

16 police suspects – 13 males and 3 females

4 juveniles – three 13-year-olds, one 15-year-old.

15 Caucasian, 1 Asian

Theft = 9, Arson = 2, Attempted rape = 1, Murder = 4

10/16 known for previous offences

FINDINGS:

 

  • Lies were accompanied by decreased blinking and increased pauses (81%)
  • No significant differences of behaviour between lying or honesty.
  • Mainly individual differences
  • 50% of liars = more head movements and speech disturbances, other 50% = showed a decrease.
  • 56% of liars = more gave aversion, other 44% = showed a decrease.

 

CONCLUSIONS:

The most reliable indicators of lying in a high-stake situation are a decrease in blinking and an increase in pauses when talking.

Strengths:

  • High ecological validity
  • Quantitative data
  • Inter-rate reliability
  • Cover observation

Weaknesses:

  • Lack of control
  • Small sample
  • Ethics
  • Difficult to replicate

 

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