VALIDITY OF SELF-REPORTED PHYSICAL WORK LOAD IN EPIDEMIOLOGIC STUDIESON MUSCULOSKELETAL DISORDERS

Objectives This study assessed the validity of self-reported physical work load by questionnaire and logbook against task analysis and obser vation. It also investigated factors (job type and low-back or neck pa in) affecting the self-assessment of physical work load and compared t he assessments between the questionnaire and the logbook. Methods A se lf-administered questionnaire including 10 questions (ordinal scales) on physical work load and musculoskeletal symptoms was filled out by 2 756 men in the forest industry. From this population, 36 men were sele cted for task analysis and observation. Logbooks including 10 continuo us variables were analyzed for 386 men. Results The Spearman rank corr elation coefficients between the self-assessments and observations for the frequency of manual handling, duration of trunk flexion, neck rot ation, hand above shoulder level, and squatting or kneeling ranged bet ween 0.42 and 0.55. The correlation coefficients for the questionnaire items were higher in general, and the accuracy better, for those with no low-back pain than for those with pain. The duration of trunk flex ion, neck flexion and hand above shoulder level was overestimated in t he questionnaires and less so in the logbooks. Conclusions Self-admini stered questionnaires may help to classify groups with heterogeneous o ccupational tasks according to some work-load factors. The accuracy of the assessments is not good for studying quantitative exposure-effect relationships, however. The logbook method might give more valid info rmation. The perception of musculoskeletal pain may bias the self-asse ssment of work load.