The Zone Comparison Test (ZCT) is one of the most widely used techniques in polygraph examinations, particularly in criminal investigations and security screenings. Developed by Cleve Backster and later adapted for federal use by the United States Army Military Police School (USAMPS) in 1961, the ZCT has undergone only minor modifications since its inception. This technique remains a cornerstone of polygraph testing, particularly within the Department of Defense Polygraph Institute (DoDPI) curriculum.

In this article, we will explore the key elements of the Zone Comparison Test, its structure, and its relevance in psychophysiological detection of deception (PDD) examinations.

Scope of the Zone Comparison Test

The ZCT is a structured polygraph examination format designed to evaluate the physiological responses of an examinee to a series of relevant and comparison questions. The test is used to determine whether the examinee is being truthful or deceptive when answering specific questions related to the issue under investigation. The ZCT is unique in that it evaluates the examinee’s responses across several “zones” of questioning, which helps to isolate the physiological reactions to different types of questions.

Pretest Phase: Establishing the Baseline

The pretest phase of the ZCT is essential for establishing rapport with the examinee and reviewing the test questions. During this phase, the examiner explains the process of the examination and ensures the examinee understands the questions that will be asked. This phase is also used to alleviate any anxiety unrelated to the test, which could otherwise skew the results.

The key questions reviewed in the ZCT include:

  1. Sacrifice Relevant (SR) Question: This prepares the examinee for the introduction of relevant questions without directly involving the issue being investigated.
  2. Relevant (R) Question: These questions directly address the matter under investigation, such as whether the examinee committed the crime.
  3. Comparison (C) Question: These are designed to elicit a physiological response for comparison with the relevant questions. Typically, they involve unrelated but morally or ethically significant matters.
  4. Irrelevant (I) Question: These questions are neutral and are used to establish a physiological baseline.
  5. Symptomatic (SYM) Question: These questions help identify whether there are other issues, not covered by the relevant questions, that are causing stress or anxiety in the examinee.

Types of Questions in the Zone Comparison Test

Primary Relevant Questions

The primary relevant questions focus directly on the examinee’s involvement in the issue under investigation. These are often repeated in different forms to ensure consistency in the physiological responses. For example:

  • R5: “Did you steal that Mustang?”
  • R7: “Did you steal that Mustang from that parking lot?”

These questions are designed to elicit a response if the examinee is lying, as the physiological responses to deception are expected to be greater when faced with these questions.

Secondary Relevant Questions

Secondary relevant questions test the examinee’s possible indirect involvement or knowledge of the issue. They are phrased to explore the examinee’s broader connection to the event, such as:

  • “Do you know for sure who stole that Mustang?”
  • “Did you help steal that Mustang?”

Secondary relevant questions are never used as substitutes for primary relevant questions but are added to assess additional layers of involvement or guilty knowledge.

Probable-Lie Comparison Questions (PLCQs)

Probable-Lie Comparison Questions are broad, unrelated questions that examine the examinee’s response to lying. They are designed to trigger a physiological reaction in truthful individuals, as they would likely be lying about minor past transgressions unrelated to the investigation. For example:

  • “Before 1997, did you ever steal anything of value?”

The purpose of these questions is to establish a baseline reaction to lying, which can be compared to the examinee’s reaction to the relevant questions.

Sacrifice Relevant Question

The Sacrifice Relevant question is a transitional question that prepares the examinee for the introduction of the primary relevant questions. This question is designed to help the examinee acclimate to the test without directly involving the issue at hand. For example:

  • “Regarding the theft of the Mustang, do you intend to answer each question truthfully?”

Data Collection and Analysis

The ZCT uses a structured approach to collecting and analyzing physiological data from the examinee. During the data collection phase, the examiner rotates the comparison and relevant questions to reduce the possibility of pattern recognition by the examinee. The goal is to measure the physiological responses consistently across several charts, which are essentially repeated sequences of questions.

The data collected from the examination is analyzed using a numerical scoring system. Each physiological response is assigned a value based on its intensity, and the comparison and relevant questions are evaluated independently. The three primary physiological responses measured include:

  • Respiration: Changes in breathing patterns.
  • Electrodermal Activity (EDA): Sweat gland activity, often measured through skin conductivity.
  • Cardiovascular Activity: Changes in heart rate and blood pressure.

Test Data Analysis and Opinion Rendering

Once the test data has been collected, the examiner uses specific criteria to render an opinion on the examinee’s truthfulness. The key criteria include:

  • Deception Indicated (DI): A score of minus three (-3) or less in any vertical spot or a grand total of minus six (-6) across all spots indicates that the examinee is likely being deceptive.
  • No Deception Indicated (NDI): A score of plus one (+1) or greater in every vertical spot with a total score of plus six (+6) across all spots suggests that the examinee is being truthful.
  • No Opinion (NO): If the results do not meet the criteria for either DI or NDI, the examiner may conclude that no definitive opinion can be rendered, except in cases of administrative issues.

Conclusion

The Zone Comparison Test is a powerful tool in the field of polygraphy, providing a systematic and reliable method for detecting deception. By using a combination of primary and secondary relevant questions, along with carefully constructed comparison questions, the ZCT allows examiners to evaluate the examinee’s physiological responses in a controlled and consistent manner. The test’s structured format and rigorous data analysis procedures help ensure the accuracy and validity of the results, making it an invaluable asset in criminal investigations and security screenings.

The careful application of the ZCT ensures that examiners can differentiate between truthful and deceptive responses with a high degree of confidence, ultimately contributing to the integrity and reliability of polygraph testing

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