Comparison of two different methods for performing combination analysis of force and posture risk factors in an epidemiological study.

Objectives: This study aimed to introduce a method of simultaneous combination analysis of multiple exposure parameters for large epidemiological studies of work-related upper-extremity musculoskeletal disorders (MSD) and compare this analysis method with the conventionally used job-level combination analysis method when applied in exposure-response analysis of work-related upper-extremity MSD.

Methods: Health outcome [carpal tunnel syndrome (CTS)] and physical exposure (forceful exertion and hand/wrist postures) data for 733 subjects were obtained from the baseline period of a 3-year work-related upper-extremity MSD study. Determinations of CTS cases were done based on a set of defined criteria. Physical exposure variables of several different types of forceful exertions and three different hand/wrist postures were collected onsite, processed, and analyzed using both a simultaneous combination and job-level combination analysis method.

Results: The commonly used job-level combination analysis method resulted in significantly different combination exposure distributions compared to the simultaneous combination analysis method, although the absolute differences were small. Both methods showed some significantly higher combined force-posture exposures among CTS cases than non-cases.

Conclusions: The simultaneous combination method provides more realistic distribution information on combined exposure parameters compared to the job-level combination method that has been commonly used in epidemiological studies. The newly developed simultaneous combination analysis method needs to be used in larger scale work-related upper-extremity MSD epidemiological studies to test its predictive power compared to the job-level combination analysis method.