Forensic Lie Detection

Question 1

Who Lies?

Daily Telegraph (1994)

Answer 1

1 in 4 tell important lies daily

1 in 12 claim never to lie

Problems with social desirability

Question 2

Who Lies?

Royal & Sun Alliance (2007)

Answer 2

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

Question 3

Who lies?

DePaulo et al 1996

Answer 3

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)

Question 4

When to use Lie Detection

Answer 4

• white lies

- more serious lies

Question 5

Who uses Lie Detection?

Answer 5

• police (lie detection)

- other professions (no less important)

Question 6

How do we measure detection accuracy?

Answer 6

Standard Methodology

How good are you?

Question 7

Human Lie Detectors

Accuracy rates in general

Answer 7

Average 54% (Bond & DePaulo 2006)

Lies - 47% accuracy
Truth - 61% accuracy

Question 8

Human Lie Detectors

Professionals

Ekman & O’Sullivan (1991)

Answer 8

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

Question 9

Truth Bias vs Lie Bias

Truth Bias

Answer 9

Everything is the truth unless we have a reason to believe otherwise.

Cognitive short-cut for non-professionals

Question 10

Truth Bias vs Lie Bias

Lie Bias

Answer 10

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

Question 11

Lie Signs

Subjective

Answer 11

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%

Question 12

Lie Signs

Objective Cues

Answer 12

• no consensus
• lack of eye contact?!
• body lang unreliable

the honest baseline…

Question 13

Physiological Lie Detection

Tyes

Answer 13

1) Voice stress analysis (Psychological Stress Evaluator)
2) The Polygraph
3) Brain Imaging

Question 14

Voice Stress Analysis

Definition

Answer 14

Lie detector tests that analyse voice changes in telephone conversations are being used to catch benefit cheats.

Question 15

Voice Stress Analysis

How does it work?

Answer 15

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.

Question 16

The Polygraph

How does it work?

Answer 16

Measures and records physiological indices: BP, pulse, respiration, skin conductivity while a person is asked a series of questions.

Deceptive answers will produce physiological responses.

Question 17

The Polygraph

Main Question Schedules

Answer 17

Control Question Technique

Guilty Knowledge Test

Other tests e.g. truth control

Question 18

Control Question Technique

Answer 18

Key advocate - Charles Honts

Compares responses to relevant questions. Control questions are designed to control for effect of generally threatening questions.

Used to arouse subjects concern about past truthfulness while relevant questions than to control questions lead to diagnosis of deception.

Question 19

Control Question Technique

Types of Question

Answer 19

Neutral
Control
Relevant

Question 20

Criticisms of CQT

Answer 20

Innocent suspects and the control questions

Subjective role of examiner

Problems with scoring

Ethical problems

False positives

Countermeasures

Question 21

Guilty Knowledge Test

Answer 21

AKA peak of tension.

Protection of innocence.
Test of knowledge that only a guilty person could possess.

MCQs

e.g. could be asked to read out list of six weapons. Show physiological response when reading out the correct weapon.

Question 22

Guilty Knowledge Test

Types of Question

Answer 22

MCQ

Answer No to all

Ignore first question responses.

Question 23

Criticisms of GKT

Answer 23

Limited applicability

• only used where facts are not widely available
• limited question generation

Memory fallibility

False Negatives

Question 24

Accuracy of the Polygraph

Answer 24

Does it work?

Types of outcome

Good result
False Positive
False Negative

Field / Experimental Study

Question 25

Accuracy of Polygraph

Stats

Vrij 2000

Answer 25

Guilty Correctly Classified

Lab CQT - 66%
Lab GKT - 96%
Field CQT - 72%
Field GKT - 96%

Question 26

Problems of Accuracy

Vrij 2000

Answer 26

False Positive

Lab CQT - 13%
Lab GKT - 4%
Field CQT - 21%
Field GKT - 4%

False Negative

Lab CQT - 9%
Lab GKT - 18%
Field CQT - 10%
Field GKT - 41%

Question 27

Applying the Polygraph

Answer 27

Polygraph in court

• not UK
• Limited USA
• Japan routinely

Used by some agencies

• USA gov’t
• UK Secret Services?
• Other countries?

Question 28

Brain Scanning and Lie Detection

Answer 28

• current play?
• fMRI
  e. g. Langleben (2008)

Brain Wave Monitoring (P300 Event-Related Brain Potentials)
e.g. Farwell 1991

BPS Working Party 2004

Question 29

Evaluation of Lie Detection Techniques?

Answer 29

Issues in accuracy and reliability