Reliability and validity of Canada's physical activity monitor for assessing trends

Purpose: This investigation assessed the reliability and criterion validity of the Physical Activity Monitor, a telephone-interview adaptation of the Minnesota Leisure Time Physical Activity Questionnaire (MLTPAQ), which is currently used to assess trends in the Canadian population. Methods: A sample of 512 people aged 18 yr and older was selected by random-digit dialing for telephone interviewing in the reliability study. The Monitor questions were administered twice, 3 wk apart. For the criterion validity study, a sample of 148 people aged 18-69 yr was selected at random from households. Participants completed the Monitor questions by telephone and an in-home step test to estimate maximum oxygen uptake. Another random sample of individuals aged 18-69 yr participated in a comparison study of the Monitor against the 1988 Campbell's Survey of Well-Being (CSWB) instrument. All studies were conducted in the vicinity of Toronto, Ontario. Spearman correlations controlling for age and sex were calculated as a measure of association for the reliability, validity, and comparison studies. Validity estimates were further adjusted for body mass index and physical activity demands of work and chores. Results: The Monitor instrument produced reliable estimates of total energy expenditure (P = 0.90, P < 0.0001) with criterion validity of 0.36 (P < 0.0001). The association between estimates of total energy expenditure derived from the Monitor and CSWB instruments was 0.77 (P < 0.0001). Conclusion: The Physical Activity Monitor has acceptable test-retest reliability and criterion validity. The research also demonstrated that for the purpose of population monitoring a change in data collection mode-telephone interview versus self-administration in households-can yield reasonably comparable estimates from two adaptations of the MLTPAQ.