| Summary: | <p>Abstract</p> <p>Background</p> <p>Single-item physical activity questions provide a quick approximation of physical activity levels. While recall questionnaires provide a more detailed picture of an individual's level of physical activity, single-item questions may be more appropriate in certain situations. The aim of this study was to evaluate two single-item physical activity questions (one absolute question and one relative question) for test-retest reliability, convergent validity, and discriminant validity, in a sample of older adults.</p> <p>Methods</p> <p>Data was obtained from the Project to Prevent Falls in Veterans, a fall risk-factor screening and modification trial. One question measured absolute physical activity (seldom, moderately, vigorously active) and one measured relative physical activity (more, about as, less active than peers). Test-retest reliability was examined using weighted Kappa statistics (κ) in a sample of 43 subjects. Validity was assessed using correlation coefficients (<it>r</it>) in participants who received clinical assessments (n = 159).</p> <p>Results</p> <p>The absolute physical activity question was more reliable than the relative physical activity question (κ = 0.75 vs. κ = 0.56). Convergent validity, however, was stronger for the relative physical activity question (<it>r </it>= 0.28 to 0.57 vs. <it>r </it>= 0.10 to 0.33). Discriminant validity was similar for both questions. For the relative physical activity question, there was moderate agreement when this question was re-administered seven days later, fair to moderate/good associations when compared with indicators of physical function, and little to no associations when compared with measures hypothesized to be theoretically not related to physical activity.</p> <p>Conclusions</p> <p>The relative physical activity question had the best combination of test-retest reliability, convergent validity and discriminant validity. In studies requiring a measure of physical activity, where physical activity is not the primary focus and more detailed measures are not feasible, a single question may be an acceptable alternative.</p>
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