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A recent commentary by Laverty and colleagues compared two recent studies1 ,2 for physical activity (PA) outcomes on groups of older adults3 and remarked that the study by Barnett et al1 had “more accurate assessment of physical activity.” Examining the referenced studies we find that the study by Barnett et al1 measured PA by self-report and the study by Godfrey et al2 measured it by an electronic body-worn monitor (BWM, accelerometry), which raises the question: Is the comparison justifiable? Evidence has shown that self-report measures of PA under/overestimate compared to gold standard (defined as electronic-based devices) measures of PA, making it difficult to attempt corrections when comparing studies.4 This highlights the inconsistency within self-reported methods of PA. If we examine the self-report method in ref. 1 we find that validity (accuracy) is modest but repeatability is high.5 This means participants are reliable in under/overestimating their PA and therefore the self-report method is ‘reliably inaccurate’. We do not question the findings of Barnett et al1 as meaning can still be derived from (large) data sets gathered in a …
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