Credibility assessment: preliminary process theory, the polygraph process, and construct validity

The term "polygraph test," particularly in a forensic context, is used generally to describe diagnostic procedures using a polygraph instrument to assess credibility. Polygraph testing has been subject to greater scrutiny, debate, and empirical study than many other forensic techniques. It has been repeatedly demonstrated that, when used properly, the polygraph testing process functions with a high degree of predictive (criterion) validity. However, advocates have failed to address, in a substantive manner, the primary objection often cited by opponents that the polygraph procedure most used in applied day-to-day contexts, that is, Comparison Question Testing (CQT), is atheoretical and lacking construct validity. A review of the available research literature, including that from the neurosciences, psychophysiology, and other relevant disciplines, coupled with an intimate understanding of two commonly used polygraph procedures, the context in which they are used, and the scientific method, strongly suggests that such claims are no longer true, nor warranted. Here, we discuss the interplay of the two most advocated polygraph procedures, the CQT and CIT (Concealed Information Testing), with Preliminary Process Theory (PPT), contemporary writings on memory and other contributions from the research literature relevant to the instrumental assessment of credibility. We conclude that the available scientific evidence not only establishes a plausible theoretical construct that strengthens the practical application of the polygraph process in forensic and other settings, but also concurrently provides directions for future research by scientists interested in the applied assessment of credibility.