Lecture 6: Polygraph
Origins of modern polygraph
● Created by William Marston, 1917
● Harvard Psychologists and Lawyer
● Use of physiological response evidence to determine innocence
● Polygraph mase more prevalent by John Larson (improved design): 1921
Polygraph: a device for recording an individual’s autonomic NS response
● 2 greek words
○ Poly = many
○ Grapho = write
Polygraph device
● ANS responses
● Pneumograph chest assembly
● Electrodermal activity (EDA)
● Blood pressure or photoelectric plethysmography
When is it used
● Police use the polygraph in police investigations insurance companies to test the
veracity of an insurance claim
● Cannot be used in court of law
● US: assess sex offenders on probation
○ Polygraph disclosure tests: uncover information on an offender’s past
○ Companies in screening employees: theft, drug use
The comparison question test (aka Control QuestionTest)
● Includes 3 types of questions
○ irrelevant= unrelated to crime (baseline)
○ relevant= concerned with rime
○ comparison= regarding person’s honesty and past history prior to event
● Pretest interview: try to convince the person that this is a valid test and we can really
tell if they are lying
○ Critical component
○ Developed control questions
○ Convince suspect of accuracy
● Interview: 10 questions, answer yes/no, relevant and comparison questions establish
guilt or innocence
○ Guilty = react more to relevant vs control
○ Innocent = react more to control vs relevant
■ Outcomes: truthful, deceptive, inconclusive
Comparison question test
Type of question
Origins of modern polygraph
● Created by William Marston, 1917
● Harvard Psychologists and Lawyer
● Use of physiological response evidence to determine innocence
● Polygraph mase more prevalent by John Larson (improved design): 1921
Polygraph: a device for recording an individual’s autonomic NS response
● 2 greek words
○ Poly = many
○ Grapho = write
Polygraph device
● ANS responses
● Pneumograph chest assembly
● Electrodermal activity (EDA)
● Blood pressure or photoelectric plethysmography
When is it used
● Police use the polygraph in police investigations insurance companies to test the
veracity of an insurance claim
● Cannot be used in court of law
● US: assess sex offenders on probation
○ Polygraph disclosure tests: uncover information on an offender’s past
○ Companies in screening employees: theft, drug use
The comparison question test (aka Control QuestionTest)
● Includes 3 types of questions
○ irrelevant= unrelated to crime (baseline)
○ relevant= concerned with rime
○ comparison= regarding person’s honesty and past history prior to event
● Pretest interview: try to convince the person that this is a valid test and we can really
tell if they are lying
○ Critical component
○ Developed control questions
○ Convince suspect of accuracy
● Interview: 10 questions, answer yes/no, relevant and comparison questions establish
guilt or innocence
○ Guilty = react more to relevant vs control
○ Innocent = react more to control vs relevant
■ Outcomes: truthful, deceptive, inconclusive
Comparison question test
Type of question
