7-position scale

What Is the 7-Position Scale?

The 7-position scale is the most widely used numerical scoring system in psychophysiological detection of deception for evaluating polygraph chart data. It provides a structured, semi-objective method for quantifying the physiological differences observed between an examinee's responses to relevant questions and comparison questions.

How Scores Are Assigned

Values in the 7-position system are whole numbers ranging from -3 to +3. Each physiological channel — electrodermal, cardiovascular, and respiratory — is scored independently at each comparison point (or "spot") on every chart presentation.

Negative Values (-1, -2, -3)

Negative scores represent greater responding to relevant questions. A -1 indicates a slight difference in favour of the relevant question, -2 a moderate difference, and -3 a dramatic difference. Consistent negative scores across charts and channels are associated with deception regarding the relevant issue.

Zero (0)

A zero indicates equal or negligible reactions to both the relevant and comparison questions at that comparison point, or that the data do not meet the minimum standards for meaningful interpretation.

Positive Values (+1, +2, +3)

Positive scores indicate greater responding to comparison questions — the pattern expected from truthful examinees in Comparison Question Technique formats. A truthful examinee's psychological concern about the comparison questions is expected to produce larger physiological responses at those points than at the relevant questions.

Scoring Variants

Three principal versions of the 7-position scale are used in professional practice, each with its own specific rules for feature evaluation:

Backster Scoring

Developed by Cleve Backster as part of the Backster Zone Comparison Technique, this version includes the distinctive Either-Or Rule for selecting which comparison question to use when scoring each relevant question.

Utah Scoring

Associated with the Utah Probable Lie Technique developed at the University of Utah, this version emphasises the Kircher Features — specific measurable aspects of the waveforms that correlate most strongly with deception.

Federal Scoring

The variant used by most U.S. federal government polygraph programmes, including the National Center for Credibility Assessment. Federal scoring incorporates elements from both the Backster and Utah approaches.

Scientific Basis

The 7-position scale is loosely based on the psychometric scaling principles developed by Rensis Likert. In the PDD literature it is sometimes described as a "semi-objective" scoring system — "semi" because while it imposes numerical structure and rules, the assignment of individual scores still involves examiner judgment in evaluating tracing features. This is one reason why blind chart analysis and inter-rater reliability studies are important quality assurance measures.

Decision Rules

Individual spot scores are aggregated across channels and chart presentations to produce total and sub-total scores. These aggregate scores are then evaluated against predetermined cut-scores to reach a final categorical outcome. Common decision rules include the Senter Rules and the evidentiary decision rules.

References

See: Bell, Raskin, Honts & Kircher (1999); Handler & Nelson (2008); Swinford (1999); Weaver (1985).