NOTES

1.  

This is the model we used to extrapolate A from reports that provided single sensitivity-specificity combinations (see Appendix H).

2.  

If A = 0.80, the false positive index is greater than 100 for any base rate below 1 in 250, and if A = 0.70, it is greater than 100 for any base rate below about 1 in 160. If the actual base rate is equal to or less than 1 in 1,000, the false positive index is at least 208 if the test has A = 0.90; at least 452 if A = 0.80; at least 634 if A = 0.70, and at least 741 if A = 0.60. Thus, if there are 10 serious security violators among 10,000 employees who are polygraphed and the criterion is set to correctly identify 8 of the 10, the test could be expected to erroneously classify as deceptive at least 1,664, 3,616, 5,072, or 5,928 of the 9,990 nonviolators, depending on which of the accuracy indexes applied to the test.

3.  

Other assumptions about the accuracy and sensitivity of polygraph testing procedures yield similarly dramatic differences between the predictive values of positive test results in screening versus event-specific investigation contexts.

4.  

A polygraph screening policy that produces 3 percent positive results, of which virtually all are false positives, will have a sensitivity of 48 percent (that is, it will correctly identify 48 percent of major violators) if the test procedure’s actual accuracy index (A) is 0.90; 25 percent if its accuracy index is 0.80; or 14 percent if its accuracy index is 0.70.

5.  

A polygraph screening policy that produces 1 percent positive results, of which virtually all are false positives, will have a sensitivity of 30 percent (identify 30 percent of the major violators) if the test procedure’s actual accuracy index (A) is 0.90; 13 percent if its accuracy index is 0.80; and 7 percent if its accuracy index is 0.70.

6.  

Polygraph testing of suspected Al Qaeda members is different from security screening of federal employees in other ways that should be recognized explicitly. Problems of language translation and of possible cultural differences in the meanings of deception and truthfulness are likely to create uncertainty in the meaning of polygraph charts and raise questions about whether these tests can be as accurate as similar tests conducted on English-speaking Americans.

7.  

We note that this criterion was rarely met in the simulation studies that have been used to assess polygraph validity for screening to date.

8.  

See United States v. Plaza, 188 F. Supp.2d 549, 2000 WL 389163 [E.D.Pa. March 13, 2002] vacating United States v. Plaza, 179 F. Supp.2d 492, 2002 WL 27305 [E.D.Pa Jan. 7, 2002].

9.  

The implications of Daubert for polygraph evidence are not straightforward. Some courts have interpreted Daubert to undermine the per se rule excluding polygraph evidence (e.g., United States v. Posado, 57 F.3d 428, 429 [5th Cir. 1995]), and some federal district courts have admitted polygraph evidence. It is reasonable to expect continued argument in the courts over whether or not the scientific evidence on polygraph testing justifies the use of test results as evidence.



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