Construct validity of a revised Physical Activity Scale and testing by cognitive interviewing

Abstract

Aim: To validate the construct validity of a new version of a Physical Activity Scale (PAS 2) for measuring average weekly physical activity of sleep, work, and leisure time to determine whether a further criterion validation is justified. Methods: The validity of responses to the questionnaire was evaluated by cognitive interviewing in 16 Danish men and women aged 21—70 years. Construct validity was validated in 342 men and women aged 35—66 years by assessing agreement between 24-h MET-scores obtained from average weekly physical activity measured by PAS 2 and a 24-h Physical Activity Scale (PAS 1), previously found to overestimate physical activity. Results: Cognitive interviewing revealed few problems in the questions on physical activity in different domains. No problems regarding the structure of the questionnaire were identified. The agreement between PAS 1 and PAS 2 MET-scores was high among participants with a PAS 1 24-h MET-score <45 MET-hours. Among participants with a PAS 1 24-h MET-score ≥45 MET-hours, the weekly-based scale, PAS 2, systematically estimated fewer MET-hours compared to the 24-h based scale, PAS 1. The difference increased proportionally with the average of the two MET-scores. Conclusions: Few, small, lexical revisions were implemented into the new scale to improve the validity. As hypothesized, PAS 2 produced lower estimates of energy expenditure compared to PAS 1, indicating that the new scale may provide more valid measurements and that further validation against an objective criterion is justified.