PDD technique developed by Cleve Backster that contains three Zones (red, green and black), with comparison of responses between two of the Zones (red and green) for a determination of truth or deception. There are several variations, including the You Phase, Exploratory, Federal Zone Comparison, Integrated Zone Comparison and Utah Probable Lie Test. The ZCT was the first modern PDD technique in general use to incorporate numerical analysis. The ZCT is probably used more often in forensic applications than any other format.

The Zone Comparison Technique (ZCT) is a psychological assessment method used primarily in the field of polygraph examination. It was developed by Cleve Backster in 1963 as an alternative to the existing polygraph techniques like the Control Question Technique (CQT). The ZCT aims to evaluate and compare physiological responses to specific types of questions to determine the truthfulness or deception of the subject undergoing the examination.

In the ZCT, the examiner divides the test into different zones, with each zone comprising a set of questions. The questions are categorized into three types:

  1. Relevant Questions: These questions pertain directly to the matter being investigated and require a truthful response from the subject.
  2. Comparison Questions: These are questions that are not directly related to the investigation but are designed to provoke a response in the subject. The comparison questions are intended to be emotionally provocative and serve as a baseline for comparison with the responses to relevant questions.
  3. Neutral Questions: These questions are unrelated to the investigation and are intended to establish a baseline physiological response. They typically cover general information or simple facts about the subject.

During the examination, the polygraph records the subject’s physiological responses to each question, including blood pressure, respiration, heart rate, and galvanic skin response. The examiner then analyzes the data to determine if there is a significant difference in the responses between the relevant and comparison questions. If the responses to the relevant questions are more pronounced than those to the comparison questions, it may indicate deception.