Factor structure of the pain disability index in workers' compensation claimants with low back injuries

Objective: To examine the factor structure of a telephone-administered Pain Disability Index (PDI) and the effects of race and sex on the PDI. Design: Computer-assisted telephone interviews of a cohort with occupational low back injuries. Setting: General community. Participants: Missouri workers' compensation claimants (N = 1329) with low back injuries. Interventions: Not applicable. Main Outcome Measures: PDI, levels of pain severity, Social Security Disability Insurance status, and the Fear-Avoidance Behavior Questionnaire. Results: Results for the total sample and by race/sex group indicated support for a 2-factor model of the PDI corresponding to voluntary activities (eg, social, occupational, recreational) and obligatory activities (eg, activities of daily living, eating, sleeping). Additional psychometric analyses of the voluntary and obligatory subscales indicated adequate reliability and construct validity overall and in each of the race/sex groups. African Americans reported more pain-related disability on both subscales than whites. Women reported more disability on the voluntary subscale than men. Conclusions: The results support use of the PDI as a bidimensional measure of pain-related disability, with strong Psychometric properties. They also support its administration by telephone.