FIGURE 5-2 Accuracy index (A) values from 52 datasets from laboratory polygraph validation studies. The central box contains the middle half of the values of accuracy (A), with the median value marked by a dot and horizontal line. “Whiskers” extend to the largest and smallest values within 1.5 interquartile ranges on either side of the box. Values farther out are marked by detached dots and horizontal lines.

Third, variability of accuracy across studies is high. This variation is likely due to a combination of several factors: “sampling variation,” that is, random fluctuation due to small sample sizes; differences in polygraph performance across testing conditions and populations of subjects; and the varying methodological strengths and weaknesses of these diverse studies. The degree of variation in results is striking. For example, in different studies, when a cutoff is used that yields a false positive rate of roughly 10 percent, the sensitivity—the proportion of guilty examinees correctly identified—ranges from 43 to 100 percent. This range is only moderately narrower, roughly 64 to 100 percent, in studies reporting a cutoff that resulted in 30 percent of truthful examinees being judged deceptive. The errors of estimate for many of the studies fail to overlap with those of many other studies, suggesting that the differences between study results are due to more than sampling variation.

We looked for explanations of this variability as a function of a variety of factors, with little success. One factor on which there has been much contention in the research is test format, specifically, comparison question versus concealed information test formats. Proponents of concealed information tests claim that this format has a different, scientifically stronger rationale than comparison question tests in those limited

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