The Lie Detector

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The Lie Detector

  1. 1. The Lie Detector Francisco J Grajales III, NBT Y http://img.dailymail.co.uk/i/pix/2008/05_04/mtpREX1405_468x427.jpg . . . . . . . . . . . . . . . . . . . .
  2. 2. Objectives and Strategies . . . . . . . . . . . . . . . . . . . . FJGIII’08 <ul><li>fMRI </li></ul><ul><li>The Gold Standard </li></ul><ul><li>Practical Predictive Value </li></ul>3. Other Techniques and Crux <ul><li>Case 1 (  Sensitivity) </li></ul><ul><li>Case 2 (  Specificity) </li></ul><ul><li>ROC Curve </li></ul>2. Evidence and Validity <ul><li>The Instrument </li></ul><ul><li>Uses </li></ul><ul><li>Assumption and Interpretation </li></ul>1. Lying and the Polygraph
  3. 3. Quiz <ul><li>The Polygraph </li></ul><ul><ul><li>Is an excellent test that should always be used to detect lying. </li></ul></ul><ul><ul><li>Is a good test that should often be used to detect lying. </li></ul></ul><ul><ul><li>Is a mediocre test which should only be used in certain situations. </li></ul></ul><ul><ul><li>Is a worthless test and should never be used to detect lying. </li></ul></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  4. 4. Quiz 2 <ul><li>True / False </li></ul><ul><ul><li>RCMP policy states: all applicants must undergo and successfully pass polygraphic examination prior to enrolment in the constabulary? </li></ul></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  5. 5. T h e I n s t r u m e n t http://www.quinn-curtis.com/polygraphUserControl11.jpg . . . . . . . . . . . . . . . . . . . . FJGIII’08
  6. 6. Uses <ul><li>Event Specific </li></ul><ul><ul><li>Did you see Mickey Mouse sexually abuse Minie? </li></ul></ul><ul><li>Employee Screening </li></ul><ul><ul><li>Have you broken patient confidentiality? </li></ul></ul><ul><li>Pre-employment screening </li></ul><ul><ul><li>Have you smoked marihuana? </li></ul></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  7. 7. Assumption and Interpretation <ul><li>Lying leads to a specific, reproducible set of physiological responses. </li></ul><ul><li>Polygraph specialist can can detect this characteristic pattern of responses. </li></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  8. 8. Evidence Case 1 8,392 2 1,598 8 A B C D 10 9,990 10,000 1,606 8,394 Spy Spy    . . . . . . . . . . . . . . . . . . . . FJGIII’08
  9. 9. Evidence Case 2 A B C D 10 9,990 10,000 41 9,959 Spy Spy    . . . . . . . . . . . . . . . . . . . . FJGIII’08 9,951 8 39 2
  10. 10. ROC Curve <ul><li>Sensitivity = 76% </li></ul><ul><li>Specificity = 63% </li></ul>Brett, A.S., Phillips, M., Beary, J.F. Predictive Power of the Polygraph . The Lancet March 8 th , 1986. P. 544-7. . . . . . . . . . . . . . . . . . . . . FJGIII’08
  11. 11. fMRI http://mri.kennedykrieger.org/images/fmri.jpg . . . . . . . . . . . . . . . . . . . . FJGIII’08
  12. 12. Gold Standard <ul><li>What is it? </li></ul><ul><li>Acceptable specificity and sensitivity ? </li></ul><ul><li>How is it tested? </li></ul><ul><li>Are there biases? </li></ul><ul><li>Is it ethical? </li></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  13. 13. Practical Predictive Value <ul><li>If gold standard is non-existent </li></ul><ul><ul><li>Then? </li></ul></ul><ul><li>Lack of follow up test </li></ul><ul><ul><li>Still valid? </li></ul></ul><ul><li>Laboratory = Real Life? </li></ul><ul><ul><li>Job loss, Humiliation, Death Penalty </li></ul></ul><ul><li>If polygraph failed </li></ul><ul><ul><li>Deception or Anxiety </li></ul></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  14. 14. Can we generalize? <ul><li>Event Specific </li></ul><ul><ul><li>Little ambiguity </li></ul></ul><ul><li>Employee Screening </li></ul><ul><ul><li>Etiology of a lie? </li></ul></ul><ul><li>Pre-employment screening </li></ul><ul><ul><li>Lying about drugs = terrorist? </li></ul></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  15. 15. Questions? <ul><li>Ciscogiii @ gmail.com </li></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08
  16. 16. Fin . . . . . . . . . . . . . . . . . . . . FJGIII’08
  17. 17. References <ul><li>Brett, A.S., Phillips, M., Beary, J.F. Predictive Power of the Polygraph . The Lancet March 8 th , 1986. P. 544-7. </li></ul><ul><li>National Academy of Sciences. The Polygraph and Lie Detection . 2003 <www.nap.edu> </li></ul><ul><li>Columbia University Medical Centre <http://www.fmri.org/fmri.htm> </li></ul><ul><li>Dictionary.com <http://dictionary.reference.com/browse/gold%20standard> </li></ul>. . . . . . . . . . . . . . . . . . . . FJGIII’08

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