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BACKGROUND: In a pilot study for the European Prospective Investigation into Cancer and Nutrition (EPIC) a modification of the Baecke questionnaire on physical activity was tested for repeatability and relative validity in a population of 134 men and women aged 20-70 years. METHODS: For the assessment of repeatability Pearson's correlation coefficients and percentages of agreement after classification in tertiles were computed between administrations of the questionnaire at baseline, and after 5 and 11 months. Relative validity was determined by comparing the questionnaire to a four times repeated 3-day activity diary. RESULTS: Repeatability after 5 and 11 months was good, with test-retest correlation coefficients between 0.65 and 0.89 for main sections of the questionnaire. The percentages of agreement, exceeding chance (Cohen's kappa) were 57% and 56% for men (at 5 and 11 months respectively) and 41% and 46% for women. The correlations with the diaries were 0.56 in men and 0.44 in women. Agreement apart from chance between classification in tertiles for both methods was 35% for men and 10% for women. CONCLUSIONS: These data show that repeatability is good and relative validity as compared to an activity diary is moderate but well within the range of values found in other studies. The questionnaire is more valid in men than in women.
Pols et al. (Sun,) studied this question.