evidentiary decision rules

What Are Evidentiary Decision Rules?

Evidentiary decision rules are decision criteria proposed by Krapohl (2005) for 7-position scoring using conservative cut-scores: a grand total of ±6 is required before declaring DI or NDI. This produces fewer definitive opinions but greater confidence in those that are rendered, with more results falling into the Inconclusive category.

Purpose

Designed for high-stakes contexts — particularly evidentiary examinations — where incorrect classification consequences are severe and a more conservative approach is warranted. By widening the inconclusive zone, both false positive and false negative errors are reduced at the cost of a higher inconclusive rate.

Comparison with Standard Rules

Standard two-stage rules use lower thresholds (±1 or ±3), producing more definitive opinions appropriate when inconclusive results carry high costs (requiring retesting or further investigation). Evidentiary rules reverse this priority: accepting more inconclusives to maximise confidence in definitive classifications. The choice between rule sets depends on the testing context and must be made before scoring begins.

Application

The APA Standards of Practice address rule selection for different contexts. For scoring method research, visit the polygraph research database.