The Polygraph

1. The Polygraph • The ideal: a machine to detect lies • No personal bias • Reliable, objective, automatic • Since 1890’s: the polygraph • A physiological measuring device • Measures several channels (heart rate, respiration, GSR, blood pressure) • In wide use worldwide • Popular in South Africa (insurance companies, recruiting) • Eg. Pick ‘n Pay, De Beers Marine, First National Bank, Kentucky Fried Chicken, SA Revenue Service

2. The polygraph A polygraph examination underway A paper recording of polygraph data (digital version similar) Actual polygraph output

3. Technology not changed since 1900s • Now it records digital • Physiological measurements are very accurate • Some sensitivity to movement, etc but can be compensated for • Can record for extended periods of time • Only measures physical variables • Not lying/innocence! • Lying is determined by making inferences about the physical measurements

4. Inferences about lying • How do you determine lying from physiological data? • No actual theory! • Basic idea: Lying will lead to increase in arousal • Increase in arousal has a particular reaction • Increase in blood pressure, heart rate, respiration • Decrease in GSR • Look for this pattern in the printout • These variables also vary naturally, often a lot

5. How to look for a lie • Look at all four channels • Any one of them may tell you • An increase will indicate an increase in arousal and thus a lie • How much of an increase indicates a lie? • Depends on each person • Must compare within subjects • Compare a ‘truth’ situation with a ‘lie’ situation • Obtain baselines • Ask subject to lie about something unrelated, check levels. • Do the same for truth telling

6. An arousal increase? • Is it true that an arousal increase goes with lying? • Assumed rather than demonstrated • Arousal increases can occur due to a number of situations • Not only lying (eg. stress about the test) • The machine cannot differentiate between these! • A problem: What do you use as your baseline? • A neutral statement • A harmless lie (?)

7. The relevant/Irrelevant test (RIT) • One way of using the polygraph • The ‘original’ way • Two types of questions asked • Simple statements, short answers (yes/no, etc) • Relevant questions (about the crime, etc) “Did you take the money?” • Irrelevant questions (used for baseline/control) “Do you live in Cape Town?” • If activity is greater in relevant questions, conclude the subject is lying • BUT: Relevant questions will lead to an increase in arousal anyway! (false positive rate is high)

8. Control Question Test (CQT) • Most common polygraph test in use • Compare critical questions with unrelated lies • Critical: “Did you take the money?” • Unrelated: “Have you ever stolen anything before this year?” • Questions discussed before the examination • If the critical response is greater than the unrelated one, conclude he was telling a lie

9. Problems with the CQT • It is necessary for the subject to believe the polygraph works • To establish the unrelated lie baseline • “stimulus test” (eg. fake card trick) • Much of the ‘effect’ of the test occurs before you begin! • Trick your subject • Examiner establishes themselves in a position of power over the subject • Great variability on results depending on the examiner • A lot depends on the questions chosen

10. Control in the CQT • The control questions (unrelated lies) are not effective controls • They do not show that the increase in critical questions can only be due to lying • The content of the critical question may greatly increase arousal in an innocent subject • The unrelated lie may not lead to significant arousal (didn’t care) • In legal disputes, critical questions will probably lead to high arousal, even in innocent subjects

11. External information in the CQT • The polygraph operator has several roles • Operates the machine • Interrogates the subject • ‘expected’ to provide the answer to the mystery • Polygrapher often knows about the case before the test • External information is used to reach a conclusion • Removes the ‘machine objectivity’ of the test • Polygraph used as a tool for coercing confessions • Should use ‘blind’ examiners only

12. Beating the polygraph • All polygraph tests work on the basis of an arousal comparison • Base state vs. lying state • You will know which questions are control questions and which are relevant • Increase arousal in control state to remove the difference • Confuses the examiner (strange pattern) • How to increase arousal • Clench leg muscles, count backwards from 100 in 13s, think of something annoying, etc. • Must do it without the examiner knowing • Will prevent non-polygraph information from being emphasized

13. So what if the theory sucks? • Even if lying/arousal is not related so what? • If the machine can detect lies, theory is irrelevant • We are solving a practical problem! • Use empirical studies to measure the usefulness of each test • The RIT does very badly • Correctly identifies lies only 50% of the time • Effective ‘guessing’ the result (coin toss would be as good) • Most researchers agree the RIT is useless to detect lies.

14. How good is the CQT? • Attracted a lot of research • Lab experiments and field studies • Confused results (±40 studies) • Lies accurately detected with 78% accuracy (53% - 90%) • Innocents accurately detected with 84% accuracy (70% - 90%) • Lab experiments have been criticized • Unrealistic (low external validity) • Perfect conditions for the machine (overestimate accuracy) • Big difference between real-world lying and lab lying

15. Field studies of CQT accuracy • Major problem: Was a lie really told? • Ground truth mostly not available • Confession or external corroboration (rare) • No clear agreement on what is acceptable to include • Iacono & Lykken (big critics) • Sampling bias in confession cases • Innocents who failed the test are omitted from the sample • Guilty cases who got away with it are not included in the sample • Studies are heavy with cases of successful identification (failures missing)

16. Field results for the CQT • Raskin & Honts (proponents of CQT) • Guilty correct identifications average 86% (73% - 100%) • Innocent correct identifications average 50%(30% - 83%) • Iacono & Lykken (oppose the CQT) • Find about the same numbers • Numbers are not very good • Average at catching liars • Very likely to generate false positives (horror!)

17. The polygraph and employment screening • Difference between criminal use and employment use • Employers want to know if a person is honest, truthful • Event-free use of the polygraph • Orwellian fantasy • People will be honest if the machine can tell when they lie! • In event free situations, the RIT is often used • The CQT designed to ask about a specific thing • RIT you can ask about anything

18. A big problem: ‘base rate’ • Types of events management wants to uncover are very rare • But the accuracy of the polygraph itself is low • This leads to extremely high false positive rates (Bayesian probability calculation) • A lot of people being turned down/fired • With 2M screenings, as many as 320 000 in the US each year (estimate mid 1980s) • USA now has a law preventing polygraph use in the workplace • But we still use it (Yay! Yay!)