Comparison of self-report and objective measures of physical activity in US adults with osteoarthritis.

To describe levels of daily physical activity and examine the extent of agreement between self-reported and objectively measured indices of physical activity, and characteristics associated with under or overestimated physical activity among persons with osteoarthritis (OA). Using cross-sectional data from the 2003-2006 National Health and Nutrition Examination Survey, we identified 533 adults ≥45 years of age with self-reported OA who completed physical activity questionnaires and had accelerometry data collected using Actigraph AM-7164. Average daily minutes of moderate to vigorous activity and 95 % confidence intervals (95 % CIs) using self-reported and objective measures were compared across sociodemographic and clinical subgroups and Spearman's rank correlations were calculated. Differences between self-reported and objectively measured moderate to vigorous activity across various personal characteristics were also estimated. Most persons with OA were non-Hispanic white (87.9 %) and women (68.9 %) with an average age of 65 years old. Self-reported measure of daily moderate to vigorous activity was on average 7 min higher compared to objective measure (17.9 vs. 10.8 min/day). Correlations between self-reported and objective measures across sociodemographic groups were mostly weak to moderate ranging from 0.01 to 0.48. Participants with higher education and better self-reported health status were more likely to over-estimate their moderate to vigorous activity using self-reported measures. Measurement methods and sociodemographic and health factors are associated with differences in reporting physical activity among persons with OA. Future research examining relationships between physical activity and health outcomes in OA should be aware of measurement issues and differences of reporting in subgroups.