Pain disability index: construct and discriminant validity.

The Pain Disability Index (PDI) was developed as a self-report measure of general and domain-specific, pain-related disability. This study's purpose was twofold: (1) to assess construct validity of the scale relative to other measures of pain-related disability and psychologic distress and (2) to assess the strength of the PDI, independent of pain intensity, in accounting for behavioral and psychologic aspects of disability. Results indicated stronger correlations for PDI factor 1 (discretionary activities) than factor 2 (obligatory activities), with factor scores significantly related to both psychologic distress and behavioral measures of disability. Partial correlation controlling for pain intensity demonstrated PDI factor 1 was significantly related to depression, employment status, and medication usage. The finding supports the usefulness of the PDI in providing important information on functional disability beyond what is provided by a simple measure of pain intensity.