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WIDUP, R. and BARLAND, G. H. Effect of the location of the numbers test on examiner decision rates in criminal psychophysiological detection of deception tests. March 1994, Report No. DoDPI94-R-0015. United States Army Criminal Investigation Command and Department of Defense Polygraph Institute, Fort McClellan, AL 36205.

The U.S. Army Criminal Investigation Command (USACIDC) conducted 251 psychophysiological detection of deception (PDD) examinations on suspects of criminal offenses in which a numbers (stim) test was conducted between the first and second tests of the main test series, as is their standard procedure. Another 231 examinations were conducted in which the numbers test was conducted prior to the first test of the main test series. Study results suggest the location of the numbers test had no effect on the inconclusive rate or the number of deception indicated (DI) and no deception indicated (NDI) decisions.

Key-words: stim test, numbers test, psychophysiological detection of deception (PDD), polygraph, forensic psychophysiology

Director's Foreword

This is another study wherein a field practitioner served as the principle investigator (PI) in conducting a field research project. One of the technical issues in psychophysiological detection of deception (PDD) has to do with the use of a numbers test in the test sequence. Some examiners use it before the main test series; others use it after the first test of the main test series; and others do not use it at all.

The results of this study support the position that it does not matter if the numbers test is used before or after the first test of the main test series as regard to an effect on the inconclusive rate or the number of deception indicated (DI) or no deception indicated (NDI) diagnostic decisions.

This study did not, however, address the issue as to the value of the numbers test as regard to whether such a test actually improves the quality of the physiological data collected and if that in turn produces higher diagnostic accuracy. In other words, does a numbers test really do what PDD examiners claim it will do? An analog study, where ground truth is known, will be required to answer this important question.

William J. Yankee, Ph.D.