FIGURE H-1 Salience scores and internal validity scores of 57 polygraph validation studies.

NOTE: Scores represent means of two (occasionally three) committee reviewers.

Correlations of internal validity score with protocol documentation and data analysis scores were 0.37 and 0.66, respectively, with a correlation of 0.30 between documentation and data analysis scores. Figure H-1 plots salience against internal validity scores, with points jittered slightly left and right to avoid overlap. A smoothing spline portrays the association.

Method of Estimating Accuracy We used the area under an ROC curve extrapolated from each dataset to summarize polygraph accuracy as manifested in that dataset. Since only one dataset gave more than two points for ROC extrapolation, an underlying model was helpful to join the small number of dots. (Here we follow the maxim, attributed to the statistician G.E.P. Box, that “all models are wrong, but some models are useful.”) The dominant model in the signal detection theory research assumes that the criterion on which decisions are based (here, the polygraph chart score) has different normal (Gaussian) distributions among groups with signal absent and present (here, nondeceptive and deceptive examinees). These distributions are presumed to have different means

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