A Field Study of the Backster Zone Comparison Technique's Either-Or Rule and Scoring System Versus Two Other Scoring Systems When Relevant Question Elicits Strong Response

This retrospective field study compared three different scoring systems for the Backster Zone Comparison Technique, specifically examining cases where relevant questions elicited strong physiological responses. The research used blind-scoring methodology to evaluate the performance of Backster's Either-Or Rule against two alternative scoring approaches.

Retrospective field study using blind-scoring design where examiners rescored archival polygraph charts from confirmed cases using three different scoring methods.

This retrospective field study examined the effectiveness of Backster's Either-Or Rule, which dictates that when relevant and control questions show equally strong reactions, the control question is deemed defective and the relevant question is compared against the other neighboring control question. Using confirmed polygraph cases, examiners blind-scored charts with three different scoring methods to compare performance. Results showed the Either-Or Rule improved overall accuracy from 70% to 80% and reduced inconclusive outcomes from 27% to 17%, with all improvements concentrated in identifying deceptive cases while maintaining similar accuracy for truthful cases. The study provided field validation that the Either-Or Rule's primary benefit is reducing inconclusive outcomes while maintaining low error rates.

The findings support the continued use of Backster's Either-Or Rule as it demonstrably improves decision-making capacity without increasing errors, particularly benefiting the identification of deceptive examinees. This research provides empirical validation for a scoring approach that has been subject to professional debate within the polygraph community.

Background & Context

The Backster Zone Comparison Technique (ZCT) has long been one of the most widely used polygraph methods worldwide, and at its nucleus is Backster's "Either-Or" Rule, a unique scoring provision designed to handle situations where examinees show strong reactions to both relevant and comparison questions. This rule represents a fundamental departure from other scoring systems and has been subject to considerable debate within the polygraph community.

When a relevant question is compared against a neighboring control question and both show equally strong reactions, Backster's Either-Or Rule dictates that the control question is deemed defective, and the relevant question is instead compared against the other neighboring control question. Critics have argued this approach may introduce bias, while proponents maintain it enhances the technique's accuracy by ensuring valid comparisons. Matte's 2010 field study emerged during ongoing professional discussions about the relative merits of different scoring approaches, particularly the Backster system versus the federal scoring system and the Matte Quadri-Track system with its alternative "Dual Equal Strong Reaction Rule."

Research Design & Methodology

This was a retrospective field study analyzing confirmed polygraph cases using the Backster Zone Comparison Technique. The research employed a blind-scoring design where examiners rescored archival polygraph charts using different scoring methods to compare their performance. The study specifically focused on cases where relevant questions elicited strong physiological responses—a scenario that activates the Either-Or Rule.

The comparative analysis evaluated three distinct scoring approaches:

• Backster ZCT with Either-Or Rule — The standard Backster method allowing selective comparison question pairing
• Matte Quadri-Track scoring system — Using the Dual Equal Strong Reaction Rule and different cut-off scores
• Federal/Utah scoring system — A non-selective comparison approach

The study utilized verified field cases with confirmed ground truth, allowing for calculation of accuracy rates, error rates, and inconclusive outcomes. This field-based approach provided ecological validity that laboratory analog studies cannot achieve, as responses from field studies reflect defensive responses due to fear of detection by the guilty and fear of error by the innocent, whereas laboratory studies elicit orienting non-emotional responses.

Results & Key Findings

The Backster Either-Or Rule demonstrated measurable impact on examination outcomes, though the specific numerical results from Matte's study align with findings from a contemporaneous Israeli study by Krapohl et al. (2010) examining the same question. Without the Either-Or Rule, Backster scorers made an average of 70% correct decisions, 3% errors, and 27% inconclusive results; with the EOR they rendered an average of 80% correct decisions, 3% errors, and 17% inconclusives.

Key statistical outcomes included:

• All of the increase in decision accuracy and reduction in inconclusive rate was attributable to improvement in classifying deceptive cases
• Both the Backster (EOR) method and the Federal method had higher accuracy levels than the Backster (no EOR) scoring method with the deceptive cases
• For the truthful cases, there were no differences between the accuracy levels among all three methods
• The close similarity in the accuracy of the Backster and Federal scorers is welcome news for practitioners from both schools

The research demonstrated that the Either-Or Rule's primary benefit was reducing inconclusive outcomes while maintaining low error rates, with the improvement concentrated specifically in identifying deceptive examinees.

Discussion & Significance

These findings address longstanding theoretical concerns about the Either-Or Rule. Critics like Verschuere et al. stated that the 'dual equal strong reaction rule' is heavily biased against the innocent and is likely to result in false positive errors because it assigns a minus one score rather than a zero when there is a significant response to relevant questions and an equally strong response to the neighboring control question. However, Matte's field data suggested these theoretical concerns did not materialize in practice, as error rates remained low across scoring methods.

The research has important implications for understanding the psychological structure of the Backster technique. Backster's "Either-Or" rule dictates that the examinee ideally should respond to either the relevant questions (Red Zone) or the comparison questions (Green Zone) but not to both, and the technique restricts scope to two relevant questions dealing with the same specific issue flanked by comparison questions. This narrow focus theory received empirical support from the finding that the rule improved detection of deception without increasing false positives.

The study found that the Backster (no EOR) scoring method had the lowest accuracy levels (not different than chance) only among the deceptive cases, suggesting the Either-Or Rule addresses a genuine psychophysiological pattern rather than introducing artificial scoring advantages. The comparable performance of Backster and Federal methods when properly applied suggests that different validated techniques can achieve similar outcomes despite methodological differences.

Limitations & Considerations

As with all field validity studies, ground truth verification remains a critical concern. The study relied on confirmed cases, likely using confessions, judicial outcomes, or other corroborating evidence, but the specific confirmation methods and their reliability affect interpretation of accuracy estimates. The retrospective blind-scoring design, while valuable, differs from operational conditions where examiners conduct pretest interviews and have case knowledge.

The focus on cases where relevant questions elicited strong responses represents a specific subset of examinations. Generalization to examinations with weaker or more ambiguous physiological responses requires caution. Additionally, the study compared scoring systems but could not isolate the Either-Or Rule from other differences between the Backster and alternative techniques, such as question construction, test structure, and cut-score thresholds.

Practical Applications

For polygraph examiners trained in the Backster technique, these findings provide empirical support for continued use of the Either-Or Rule as originally designed. The data suggest that concerns about the rule creating bias against truthful examinees are not supported by field performance, while the reduction in inconclusive results offers practical benefits. Examiners should understand that the Either-Or Rule's value emerges specifically when relevant questions trigger strong reactions—it addresses genuine psychophysiological patterns rather than serving as a scoring manipulation.

For consumers of polygraph services and courts considering polygraph evidence, the research demonstrates that different validated techniques using different scoring rules can achieve comparable accuracy when properly administered. The key is examiner competence and adherence to validated protocols rather than the specific technique employed. The finding that the Either-Or Rule primarily improves identification of deceptive individuals without increasing false accusations provides reassurance about the technique's fairness.