Demographic effects (sex and parenthood status) on the level of association between self-reported and accelerometer assessed physical activity were examined among a large diverse sample of adults. Participants (N = 1,249, aged 20 - 65 years) wore accelerometers (Actical) for 7 days and completed an interviewer-administered physical activity recall questionnaire (IPAQ- LF) for the same period. Mean daily minutes of moderate physical activity (MPA) and moderate to vigorous physical activity (MVPA) were used in analyses. Linearity between methods was explored by regressing mean minutes of activity and Pearson’s correlations were performed. A weak association between IPAQ-LF and Actical minutes of MPA and MVPA per day was shown for the whole sample (rs = 0.216 – 0.260). The magnitude of association varied between males (rs = 0.265 – 0.366) and females (rs = 0.124 – 0.167), although no obvious variations in associations were evident for parenting status. The IPAQ-LF produced substantially greater variations in estimates of physical activity than that recorded by the Actical accelerometer and large discrepancies between methods were observed at an individual level. Self-report tools provide a poor proxy of overall human movement, particularly among females. Inferences made at an individual level from self-reported data, such as intervention efficacy or health outcomes, may have substantial error.
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