System of assigning values to individual physiological responses in PDD, based on differential responding to relevant and comparison questions. The values in 7-position scoring are whole numbers between -3 and +3. By convention, negative values represent greater responding to relevant questions, while positive values indicate greater responses to comparison questions. A zero usually indicates equal or no reactions to the relevant and comparison questions, or that the spot does not meet minimum standards for interpretation. In the PDD literature, the 7-position scale is sometimes referred to as a semi-objective scoring system and is loosely based on the psychometric scales developed by Rensis Likert. There are three major versions of the 7position scoring system: Backster, Utah, and Federal. See: Bell, Raskin, Honts, & Kircher (1999); Handler & Nelson (2008); Swinford (1999); Weaver (1985).