Reliability and validity of a modified self-administered version of the Active Australia physical activity survey in a sample of mid-age women

Objective: To assess the test-retest reliability and validity of a modified self-administered version of the Active Australia physical activity survey. Methods: One hundred and fifty-nine mid-age women (54-59 years) completed a mailed physical activity questionnaire before recording daily pedometer step counts for seven consecutive days. A random subsample (n=44) also wore an accelerometer during this period. Participants then completed the physical activity questionnaire again. Spearman's rho and per cent agreement were used to assess test-retest reliability. Self-reported physical activity data (time 2) were compared with pedometer and accelerometer data using box plots and Spearman's correlations to assess validity. Results: Median time between surveys was 13 days. Median frequency and duration of moderate and vigorous physical activity were the same at both surveys, but median walking frequency was slightly higher at time 2 than time 1. Reliability coefficients for frequency/time in each domain of physical activity ranged from 0.56-0.64 and per cent agreement scores ranged from 40% to 65% for the physical activity categories; agreement was 76% for 'meeting guidelines'. Correlations (p) between self-reported physical activity and 1) weekly pedometer steps and 2) accelerometer data for duration of at least moderate intensity physical activity were 0.43 and 0.52 respectively. Conclusions: The measurement properties of this modified self-administered physical activity survey are similar to those reported for the original computer assisted telephone interview survey. Implications: This modified version of the Active Australia survey is suitable for use in self-administered format.