Repeatability and relative validity of two physical activity questionnaires in elderly women.

In a population of 33 women aged 51-71 yr, two physical activity questionnaires (a modified Baecke questionnaire and the pre-EPIC questionnaire) were tested for repeatability (5 and 11 months). For assessment of relative validity, the questionnaires were compared with a physical activity diary (12 d) as the main reference method, a single 24-h Caltrac accelerometer score, and energy intake estimated from a 24-h dietary recall repeated 12 times. Repeatability of the questionnaires at 5 months was 0.82 (Baecke) and 0.42 (pre-EPIC), at 11 months 0.73 and 0.60, respectively. Correlation with the activity diary was 0.51 for the Baecke and 0.64 for the pre-EPIC questionnaire. Correlation with the Caltrac was 0.22 for both questionnaires, and with energy intake -0.21 and 0.43, respectively. Factor analysis suggested that the questionnaires and the diary measured a common aspect of activity, which could be interpreted as "reported normal physical activity." Women who reported sweating or breathlessness during the past week scored significantly higher only on the Baecke questionnaire. It was concluded that the two questionnaires seemed to be able to rank older women according to physical activity in epidemiological studies.