Convergent validity of a brief self-reported physical activity questionnaire

The objective of this study is to determine whether summary estimates of a self-report physical activity questionnaire that does not specifically assess frequency or duration (the Coronary Artery Risk Development in Young Adults (CARDIA) physical activity history (PAH)) differs from the summary estimates of one that does (CARDIA Supplemental Questionnaire).

After the year 25 examination (2010-2011), 203 CARDIA black and white men and women (age 50.3 ± 3.6 yr) at the Oakland, CA, site participated in this comparison study. The between-questionnaire association and agreement were determined for continuous and categorical estimates on the basis of 1) quartiles and 2) meeting 2008 physical activity guidelines. Differences in participant characteristics by concordance/discordance status were also examined. Finally, receiver operating characteristic curves were computed to determine the accuracy of the PAH compared with the supplemental questionnaire.

Reported physical activity levels were high and varied significantly by race and sex (all P < 0.01). Between-questionnaire estimates were significantly correlated (rho = 0.75 to 0.90, all P < 0.001) and had high agreement (κ = 0.51 to 0.80) across all race/sex groups. A higher proportion of women than men were classified as concordant by quartile of vigorous intensity (P = 0.001), but no other participant characteristics were associated with concordant/discordant quartile ranking. Participants classified as concordant on the basis of physical activity guidelines had lower body mass index than those classified as discordant (both P < 0.05). The area under the curve was 0.95, suggesting that the PAH has high accuracy for classifying individuals as meeting physical activity guidelines.

Although it is inconvenient that the PAH is not expressed in more standard units, these findings support the practice of not directly assessing frequency and duration, which are frequent sources of reporting error.