Reliability and validity of the PAD questionnaire: a measure to assess pain-related decline in physical activity.

OBJECTIVE: To examine the reliability and validity of the physical activity decline (PAD) score: a measure for assessing a decline in the level of physical activity in patients with chronic pain. DESIGN: This study was embedded in a prognostic cohort study based on an inception cohort of patients with sub-acute low back pain. PATIENTS: Sixty-two patients who developed chronic pain participated in this study. METHODS: Internal consistency was expressed by Cronbach's alpha and the test-retest reliability was based on an intraclass coefficient (ICC) score. Construct validity was determined using a Pearson correlation coefficient with disability (Quebec Back Pain Disability Scale), a change in physical activity level (DeltaBPAQ) as external criteria for convergent validity. The level of physical activity (Physical Activity Rating Scale) was used as external criterion for discriminant validity. RESULTS: The internal consistency (Cronbach's alpha = 0.92) and reliability (ICC = 0.93) of PAD were shown to be good. The construct-validity of the PAD questionnaire appeared to be adequate, with Pearson coefficients of r = 0.45 (p < 0.01; a change in BPAQ), r = 0.55 (p < 0.01; disability) and r = 0.03 (p = 0.74; physical activity). Based on the fact that 38.7% of the patients had the lowest score of 0, the presence of a floor-effect in the PAD score must be considered. CONCLUSION: The reliability and validity of the PAD questionnaire in its original Dutch version appears to be good. Further research is warranted regarding the presence of a floor-effect.