Questionnaire-based mechanical exposure indices for large population studies - reliability, internal consistency and predictive validity

Objectives This study attempts to construct valid indices for mechanical ex posure of the shoulder neck region with relation to the development of shou lder-neck pain in a 1-year perspective study of a general population. Methods A comprehensive questionnaire was presented to 14 556 subjects aged 45 or 65 years and repeated after 12 months. Twenty-four questions concern ing positions, movements, and manual materials handling were registered on a 3-point impact scale. Musculoskeletal problems were reported on a slightl y modified version of the Standardized Nordic Questionnaire for the Analysi s of Musculoskeletal Symptoms. Test-retest stability after 2 weeks was calc ulated for 232 consecutive participants. Based on mechanistic theories, 4 e xposure indices were formed. Another 5 constructs were obtained by factor a nalysis. Results All the indices showed good test-retest stability, and 5 of them ha d very good internal consistency. Due to overlaps between the indices, 2 in dices stood out as having unique properties. One of them concerned mainly p ostures and the other dealt primarily with measured lifting. However, the l atter was not related to the shoulder-neck pain outcome when adjusted for t he posture index. The posture index showed an exposure-effect relationship with the outcome. The job titles implied a large degree of exposure misclas sification. Conclusions The posture index is recommended as a mechanical exposure index for analyses of interaction with other possible determinants of shoulder-n eck pain (ie, psychosocial factors). The use of such an index instead of jo b titles in large population studies will reduce the risk of misclassificat ion.