Forensic Lie Detection Flashcards
Who Lies?
Daily Telegraph (1994)
1 in 4 tell important lies daily
1 in 12 claim never to lie
Problems with social desirability
Who Lies?
Royal & Sun Alliance (2007)
Do we tell more lies a decade later?
45% were prepared to lie to their boss.
41% admitted they would lie to their friends.
20% said they had lied to an insurance company
38% claimed they had never told a lie
Who lies?
DePaulo et al 1996
Using diary
Students lie x2 day 1 in 3
Community members lie 1x day / 1 in 5
Who do we lie to?
Romantic partners 1 in 3
Spouses 1 in 10
Student - Mother 1 in 2
How do we tell our lies?
Face to Face 85%(s)/72%(c)
Telephone 14%(s)/28%(c)
Written 1%(s)/<0.05%(c)
When to use Lie Detection
- white lies
- more serious lies
Who uses Lie Detection?
- police (lie detection)
- other professions (no less important)
How do we measure detection accuracy?
Standard Methodology
How good are you?
Human Lie Detectors
Accuracy rates in general
Average 54% (Bond & DePaulo 2006)
Lies - 47% accuracy
Truth - 61% accuracy
Human Lie Detectors
Professionals
Ekman & O’Sullivan (1991)
Secret Service - 64.12 Federal Polygraphers - 55.79 Robbery Investigators - 55.79 Judges - 56.73 Psychiatrists 57.61 Special Interest 55.34 College students 52.82
Truth Bias vs Lie Bias
Truth Bias
Everything is the truth unless we have a reason to believe otherwise.
Cognitive short-cut for non-professionals
Truth Bias vs Lie Bias
Lie Bias
Ekman (2001)
Police and social workers “think that nearly everyone they see is guilty and everyone is lying”
No one ever tells the truth
Possibly not using correct cues
Lie Signs
Subjective
Lack of eye contact
Global Deception Research team 2006 - in 51 of the 58 countries we studied, gaze aversion is more prevalent than any other belief about lying.
71.5% of respondents worldwide believe that liars would avoid eye contact.
43% mention first cue of lying
Nervous body shifting 65.2%
Lie Signs
Objective Cues
- no consensus
- lack of eye contact?!
- body lang unreliable
the honest baseline…
Physiological Lie Detection
Tyes
1) Voice stress analysis (Psychological Stress Evaluator)
2) The Polygraph
3) Brain Imaging
Voice Stress Analysis
Definition
Lie detector tests that analyse voice changes in telephone conversations are being used to catch benefit cheats.
Voice Stress Analysis
How does it work?
Records voice using a microphone and based on tenent non-verbal, low frequency content of the voice conveys information and psychological state of speaker.
Aims to differentiate between stressed and non-stressed outputs in response to stimuli with high stress seen as indication of deception.
