Polygraph techniques can be divided into two major categories, knowledge-based tests, also called recognition tests, and deception-based tests. The recognition test family of PDD techniques includes the Peak of Tension test, acquaintance test and concealed information test. Recognition tests attempt to determine if the examinee has knowledge only available to persons directly involved in an incident of concern. Because this approach depends upon the existence of a known crime or incident facts that remain unknown to the innocent suspect, the recognition test paradigm is not suited for use as a screening test. See: Krapohl, McCloughan & Senter (2006); Lykken (1959); Osugi (2011).