ABSTRACT
Aims: In epidemiological studies exposure assessment based on questionnaires is the most cost-effective method. A question about lifetime exposure to occupational physical activity (OPA) was used in a population-based survey (part of the Copenhagen Aging and Midlife Biobank, CAMB). The aim of the study was to validate this question through a three-step process. Methodology: Firstly, the response process was studied by cognitive interviewing of 7 persons. Secondly, 64 persons participated in semi-structured interviews about their work-life, and expert judgments of exposure to OPA were compared with questionnaire-data. Exposure was 20 years of work in one of four categories of OPA: sedentary, standing and walking, moderate or high OPA. Kappa values were calculated for agreement and interpreted according to Landis and Koch’s criteria. Agreement was visualized in Bland-Altman plots. Thirdly, intra- and inter-rater reliability of expert judgments was tested. Results: Response process: The question had a complicated instruction, and the respondents found it hard to remember, categorize, and summate exposures. Semi-structured interviews: Kappa value for exposure to sedentary work was ‘substantial’ (0.71) but ‘fair’ for the other categories of OPA (0.27-0.29). Agreement between questionnaire and interview was higher in sedentary jobs and jobs with high OPA. Intra-rater reliability of expert judgments was ‘substantial’ or ‘moderate’ (0.60-0.71). Inter-rater reliability was high in sedentary jobs but lower in the more active jobs. Conclusion: Self-reports of lifetime exposure to sedentary work are valid in the CAMB cohort, whereas the validity of self-reports of exposure to high levels of occupational physical activity (OPA) are questionable. Thorough pre-testing of questions about lifetime OPA is recommended.