Validation of questions on working posture among those who stand during most of the work day

The present study tests the validity of work posture questions derived from the 1998 Quebec Health and Social Survey and administered to 92 factory, laundry, hospital, and blue collar public service workers in Montreal, Quebec, Canada. Subjects who had usually stood during their workday reported retrospectively on their mobility: usual movement within a 1-m radius; within a 5-m radius; over 5 m. They were also asked whether they could sit down at will, occasionally or never. Observers recorded working posture continuously throughout the workday and also answered the same questions as the workers at the end of the workday. Using observer estimates as the "gold standard", validity was good for the question on mobility (Cohen's weighted kappa = 0.60, concordance 70.1%) and for the question on freedom to sit (Cohen's kappa = 0.72, concordance 85.9%). The response categories for both questions distinguished between different types of exposure to standing, walking and sitting, as measured by the recorded work activity. Self-reports of worker mobility and control over working posture may be a useful addition to questionnaires in studies relating working conditions to musculoskeletal and cardiovascular outcomes, if exposure categories are well defined.