Purpose: To determine whether respondents share researchers' understandings of concepts and questions frequently used in the assessment of usual physical activity (PA) behavior.
Methods: As part of On the Move, a study aimed at reducing measurement error in self-reported physical activity (PA), we conducted cognitive interviews with 19 men and 21 women, ages 45-65, regarding their responses to the PA questionnaires used in two large, population-based studies, Life After Cancer Epidemiology and California Men's Health study. One questionnaire asks about the frequency, the duration, and the perceived intensity of a range of specific activities in several different domains over the past 12 months. The second questionnaire asks about frequency and duration of specific, mostly recreational activities, grouped by intensity (i.e., moderate or vigorous) over the past 3 months. We used verbal probing techniques to allow respondents to describe their thought processes as they completed the questionnaires. All interviews were tape-recorded and transcribed, and the transcripts were then analyzed using standard qualitative methods.
Results: Cognitive interviews demonstrated that a sizable number of respondents understood "intensity" in terms of emotional or psychological intensity rather than physical effort. As a result, the perceived intensity with which a participant reported doing a specific activity often bore little relationship to the MET value of that activity. Additionally, participants often counted the same activity more than once, overestimated work-related PA, and understood activities that were grouped together in a single category to be definitive lists rather than examples.
Conclusion: Cognitive interviews revealed significant gaps between respondents' interpretations of some PA questions and researchers' assumptions about what those questions were intended to measure. Some sources of measurement error in self-reported PA may be minimized by additional research that focuses on the cognitive processes required to respond to PA questionnaires.