the field system to develop models suggesting what actual manipulation might produce.

The relevance of the available research to security screening applications is far less than would be desirable. Only one flawed study investigates a real polygraph screening program, and the simulated screening studies are too closely tied to specific mock crimes to simulate adequately the generic nature of polygraph screening questions. Moreover, all of the studies available to us were conducted on samples with base rates of guilt far above the extremely low rates typical of employee security screening programs, so that generalization from those studies to screening applications is quite problematic. (We address the base rate problem in detail in Chapter 7.)

LABORATORY STUDIES

For a variety of understandable practical reasons, the great majority of polygraph validation studies have been laboratory based. This research has consisted predominantly of efforts to measure test accuracy in simulated settings or compare accuracy across methods of testing or test interpretation. There has been relatively little attention to issues of theory, as noted in Chapter 3. For instance, very few studies have investigated threats to validity that seem potentially important on theoretical grounds, such as effects of stigma and expectancy. As a result, serious open questions remain about the basis for generalizing beyond the laboratory situations. The laboratory studies are also inconsistent regarding their attention to methodological controls. We found numerous studies that provide tight control in one or more respects but omit control in others. In addition, most studies have presented the data in terms of one or two cutoff points for scoring, preventing exploration of how the tradeoff between false positives and false negatives might vary with slightly different applications of the same testing approach. Although valuable laboratory studies have been done, they are relatively few in number and leave us with limited enthusiasm for this body of research as a whole.

EXPERIMENTAL FIELD STUDIES

The most compelling type of field validation study is an experimental field study, one in which a variable of interest is manipulated among polygraph examinations given in a real-life polygraph testing context, for example, the context of an actual security screening program. The variable of greatest interest is usually guilt/innocence or deception/truthfulness on relevant questions, a variable that is difficult, though not impossible, to manipulate in a field setting. Other variables are also of



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