The Polygraph and Lie Detection (2003) / Chapter Skim
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7 Uses of Polygraph Tests
7 Uses of Polygraph Tests
Pages 178-211
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From page 178... ...
This chapter discusses the policy issues involved in using an imperfect diagnostic test such as the polygraph in real-life decision making, particularly in national security screening, which presents very difficult tradeoffs between falsely judging innocent employees deceptive and leaving major security threats undetected. We synthesize what science can offer to inform the policy decisions, but emphasize that the choices ultimately must depend on a series of value judgments incorporating a weighting of potential benefits (chiefly, deterring and detecting potential spies, saboteurs, terrorists, or other major security threats)
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From page 179... ...
The prospect of false positive results can also have this effect if employees resign or prospective employees do not seek employment because of polygraph screening. As Chapter 2 shows, polygraph tests, like any imperfect diagnostic tests, yield both false positive and false negative results.
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From page 180... ...
Tradeoffs between false positives and false negatives can be calculated mathematically, using Bayes' theorem (Weinstein and Fineberg, 1980; Lindley, 1998~. One useful way to characterize the tradeoff in security screening is with a single number that we call the false positive index: the number of false positive cases to be expected for each deceptive individual correctly identified by a test.
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From page 181... ...
Figures 7-1 and 7-2 show that the tradeoffs involved in relying on a diagnostic test such as the polygraph, represented by the false positive index values on the vertical axis, are sharply different in situations with high base rates typical of event-specific investigations, when all examinees are identified as likely suspects, and the base rate is usually above 10 percent, than in security screening contexts, when the base rate is normally very low for the most serious infractions. The false positive index is 200 1 801 601 4 0 1 2 0 .~ 1 000' 8 0 O 6 0 40 i\ 80% 50% 20% _ ~~NNNNNNNNNNNNNNNNNNNNNNNNN~ | 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 Base Rate of Poor Security Risks FIGURE 7-1 Comparison of the false positive index and base rate for three sensitivity values of a polygraph test protocol with an accuracy index (A)
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From page 182... ...
For example, a test with an accuracy index of 0.90, if used to detect 80 percent of major security risks, would be expected to falsely judge about 200 innocent people as deceptive for each security risk correctly identified. Unfortunately, polygraph performance in field screening situations is highly unlikely to achieve an accuracy index of 0.90; consequently, the ratio of false positives to true positives is likely to be even higher than 200 when this level of sensitivity is used.
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From page 183... ...
In this example, the false positive index is higher than 100 for any base rate below about 1 in 500, even with A = 0.90. That is, if 20 of 10,000 employees were serious security violators, and polygraph tests of that accuracy were given to all 10,000 with a threshold set to correctly identify 16 of the 20 deceptive employees, the tests would also be expected to identify about 1,600 of the 9,980 good security risks as deceptive.2 Another way to think about the effects of setting a threshold that correctly detects a very large proportion of deceptive examiners is in terms of the likelihood that an examinee who is judged deceptive on the
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From page 184... ...
If the base rate of deceptive individuals in a population of examiners is 1 in 1,000, an individual who is judged deceptive on the test will in fact be nondeceptive more than 199 times out of 200, even if the test has A = 0.90, which is highly unlikely for the polygraph (the actual numbers of true and false positives in our hypothetical population are shown in the right half of part a of Table 2-1~. Thus, a result that is taken as indicating deception on such a test does so only with a very small probability.
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From page 185... ...
Thus' using the polygraph with a "suspicious" threshold so as to catch most of the major security threats creates a serious false-positive problem in employee security screening applications, mainly because of the very low base rate of guilt among those likely to be screened. When the base rate is one in 1,000 or less, one can expect a polygraph test with a threshold that correctly identifies 80 percent of deceptive examiners to incorrectly classify at least 100 nondeceptive individuals as deceptive for each security threat correctly identified.
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From page 186... ...
Department of Energy, appear to adopt fairly "friendly" effective thresholds, judged by the low proportion of polygraph tests that show significant response. The net result is that these screening programs identify a relatively modest number of cases to be investigated further, with few decisions eventually being made that the employee has been deceptive about a major security infraction.
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From page 187... ...
In our judgment, the accuracy of polygraph testing in distinguishing actual or potential security violators from innocent test takers is insufficient to justify reliance on its use in employee screening in federal agencies. Although we believe it likely that polygraph testing has utility in screening contexts because it might have a deterrent effect, we were struck by the lack of scientific evidence concerning the factors that might produce or inhibit deterrence.
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From page 188... ...
The Webster Commission clearly wants to avoid a repetition of this situation at the FBI. It recommends that "adverse personnel actions should not be taken solely on the basis of polygraph results," a position that is absolutely consistent with the scientific evidence that false positives cannot be avoided and that in security screening applications, the great majority of positives will turn out to be false.
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From page 189... ...
, we believe there is a widespread belief in this community that someone who "passes" the polygraph is "cleared" of suspicion. Acting on such a belief with security screening polygraph results could pose a danger to the national security because a negative polygraph result provides little additional information on deceptiveness, beyond the knowledge that very few examiners are major violators, especially when the test protocol produces a very small percentage of positive test results.
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From page 190... ...
Making Tradeoffs Because of the limitations of polygraph accuracy for field screening applications, policy makers face very unpleasant tradeoffs when screening for target transgressions with very low base rates. We have summarized what is known about the likely frequencies of false positive and false negative results under a range of conditions.
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From page 191... ...
Other Potential Uses of Polygraph Tests The above discussion considered the tradeoffs associated with polygraph testing in employee security screening situations in which the base rate of the target transgressions is extremely low and there is no specific transgression that can be the focus of relevant questions on a polygraph test. The tradeoffs are different in other applications, and the value of polygraph testing should be judged on the basis of an assessment of the aspects of the particular situation that are relevant to polygraph testing
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From page 192... ...
We have already discussed the effects of base rate on the tradeoffs involved in making decisions from polygraph tests and the way the use of polygraph testing as an aid to decision making becomes drastically less attractive as the base rate drops below a few percent. The costs of false positive and false negative errors are also important to consider in making policy choices.
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From page 193... ...
An illustrative example is posed by the need to screen of hundreds of detainees captured in Afghanistan in late 2001 to identify those, perhaps a sizable proportion, who were in fact part of the A1 Qaeda terrorist network. Such a focused screening situation is like typical security screening in that there is no specific event being investigated, but it is different in that it may be possible to ask specific relevant questions, including questions of the concealed information variety.6 It is thus possible to use concealed information polygraph tests or other tests that require the same format and that are not appropriate for screening situations in which specific questions cannot be constructed.
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From page 194... ...
A polygraph or other screening procedure that is inappropriate or inadvisable for employee security screening may be more attractive in some focused screening situations. As with other applications, the tradeoffs should be assessed and the judgment made on how and whether to use polygraph screening on the basis of the specifics of the particular situation.
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From page 195... ...
First, reliable test administration and interpretation are both desirable in a testing program and essential if the program is to have scientific standing. Second, however, it is critical to remember that reliability, no matter how well ensured, does not confer validity on a polygraph screening program.
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From page 196... ...
the existing computerized algorithms for polygraph scoring, both at JHU-APL and elsewhere, (b) the one problematic effort at external independent validation carried out by DoDPI (Dollins, Kraphol, and Dutton, 2000)
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From page 197... ...
Little evidence is available from the research literature on polygraph testing concerning this possibility, but until definitive evidence is available, it might be wise to include both computerized scoring and independent hand scoring as inputs to a decision process. Combining Polygraph Results with Other Information In most screening applications, information from polygraph examinations (chart and interview information)
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From page 198... ...
It makes sense to use the polygraph in security screening if it adds information relevant to detecting security risks that is not otherwise available and with acceptable tradeoffs. Federal agencies use or could use a variety of information sources in conjunction with polygraph tests for making personnel security decisions: background investigations, ongoing security checks by various investigative techniques, interviews, psychological tests, and so forth (see Chapter 6~.
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From page 199... ...
Most of those who test positive will be false positives, especially if the condition has a low base rate. In this approach, people who test positive are then subject to a more accurate but more expensive or invasive second-stage test, and so on through as many stages as warranted.
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From page 200... ...
If the purpose of using the polygraph is like that of cancer screening to avoid false negatives the threshold should be set so as to catch a high proportion of spies or terrorists. The result of this approach, in a population with a low base rate of spies or terrorists, is to greatly increase the number of false positives and the accompanying expense of investigating all the positives with traditional methods.
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From page 201... ...
Lacking such knowledge, the serious problems that exist in deriving and adequately validating procedures for computer scoring of polygraph tests (discussed above) also exist for the derivation and validation of expert systems for combining polygraph results with other diagnostic information.
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From page 202... ...
The basic difference between Frye and Daubert is one of perspective: courts using Frye are deferential to the particular fields generating the expertise, whereas Daubert places the burden on the courts to evaluate the scientific validity of the expert opinion. This difference of perspective has begun to significantly change the reception of the scientific approach in the courtroom.9 Much of the expert opinion that has been presented as "scientific" in courts is not based on what scientists recognize as solid scientific evidence, or even, in some cases, rudimentary scientific methods and prin
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From page 203... ...
In fact, topics such as bite mark and hair identification, fingerprinting, arson investigation, and tool mark analysis have a less extensive record of research on accuracy than does polygraph testing. Historically, the courts relied on experts in sundry fields in which the basis for the expert opinion is primarily assertion rather than scientific testing and in which the value of the expertise is measured by effectiveness in court rather than scientific demonstration of accuracy or validity.
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From page 204... ...
Concealed information polygraph tests, for example, have limited usefulness as a screening device simply because examiners usually cannot create specific questions
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From page 205... ...
The legal meaning of a comparison question test polygraph report might be different if the expert opinion is presented in terms of whether the examinee showed "significant response" to relevant questions, rather than in terms of whether the responses "indicated deception." Significant response is an inferential step away from any conclusion about credibility, in the sense that it is possible to offer innocent explanations of "significant response," based on various psychological and physiological phenomena that might lead to a false positive test result. When courts assess the value of forensic tools, the consequences that follow a "positive" or "negative" outcome on the test are important.
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From page 206... ...
This is a relatively straightforward assessment. Polygraph tests, however, have been advocated variously as lie detectors and as aids for interrogation.
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From page 207... ...
However, if the courts only consider the expert opinions of forensic odontologists who do bite mark identifications for police laboratories, they are unlikely to get a full view of the value of this kind of evidence. Unfortunately, in many fields of forensic science there are no communities of scientists conducting basic research and the only people who are asked as expert witnesses are interested practitioners with little proficiency in scientific methods.
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From page 208... ...
Even those who believe the polygraph "works" adequately in a criminal investigation should not presume without further careful analysis that this justifies its use for security screening. Given the very low base rates of major security violations, such as espionage, that almost certainly exist in settings such as the national weapons laboratories, as well as the scientifically plausible accuracy level of polygraph testing, polygraph screening is likely to identify at least hundreds of innocent employees as guilty for each spy or other major security threat correctly identified.
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From page 209... ...
The tradeoffs presented by polygraph testing vary with the application. For example, some focused screening applications may present more favorable tradeoffs for polygraph use than those involved in employee security screening in the DOE laboratories.
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From page 210... ...
Assessments of the polygraph for the purposes of forensic science should take into account the test's design, function, and purpose because both the accuracy of the test and the practical meaning of particular accuracy levels are likely to depend on these factors.
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From page 211... ...
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)
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