Criterion validity of a 10-category scale for ranking physical activity in Norwegian women

A sample of 177 randomly recruited healthy women attended two clinical visits approximately 4-6 months apart. At each visit, the women completed the NOWAC PA questionnaire (NOPAQ), rating their overall PA level on a 10-category scale (1 being a "very low" and 10 being a "very high" PA level) and performed an 8-minute step-test to estimate aerobic fitness (VO2max). After each visit, the women wore a combined heart rate and movement sensor for 4 consecutive days of free-living. Measures of PA obtained from the combined heart rate and movement sensor, which were used as criterion, included individually calibrated PA energy expenditure (PAEE), acceleration, and hours/day of moderate-to-vigorous intensity PA (MVPA). These were averaged between visits and compared to NOPAQ scores at visit 2.Intra-class correlation coefficients for objective measures from both free-living periods were in the range of 0.65-0.87 (P < 0.001), compared to 0.62 (P < 0.001) for NOPAQ. There was a moderate but significant (P < 0.001) Spearman's rank correlation coefficient in the range of 0.36-0.46 between NOPAQ and objective measures of PA. Linear trends for the association between the NOPAQ rating scale with PAEE, hours/day of MVPA and VO2max (P < 0.001) were also demonstrated.Self-reported PA level measured on a 10-category scale appears valid to rank PA in a female Norwegian population.In large-scale epidemiologic studies, physical activity (PA) is often assessed using questionnaires [1,2]. Self-report methods as global questionnaires are commonly used to assess the relationship with health outcomes in order to rank or classify individuals as either physically active or inactive [3,4]. Indeed, a number of different PA questionnaires have been developed for various purposes such as surveillance, etiological investigation and risk stratification [5]. PA is a complex multidimensional behavior characterized in terms of volume, domain, type, duration, intensity and frequency [6], which makes PA in