PDD scoring rule forwarded by Cleve Backster and used exclusively in the Backster Zone Comparison Technique. According to the rule, if a relevant question does not evoke a physiological reaction, it is scored against the adjacent comparison question with the larger reaction. If the relevant question does produce a significant reaction, it is compared to the comparison question with the smaller reaction. See: Matte (1996); Meiron, Krapohl & Ashkenazi (2008).