Constructing and Validating an Occupational Mechanical Job Exposure Index (MJEI) Based on Five Norwegian Nationwide Survey of Living Conditions on Work Environment

Background: The aim of this study is to (i) construct and validate a job exposure index for mechanical job exposures and (ii) test its predictive validity for individual reported lower back pain and long-term sick absence, as well as disability benefits, long-term sick leave and mortality using register data. Methods: We utilize data from the Norwegian nationwide Survey of Living Conditions on work environment in 2006, 2009, 2013, 2016 and 2019. Occupations are classified on a 4-digit level based on the Norwegian version of the International Standard Classification of Occupations (ISCO-88). We constructed a 4-digit correspondence table between the occupational codes used in the 2006 and 2009 surveys (STYRK-98) and the codes used in 2013, 2016 and 2019 (STYRK-08). The mechanical exposures were collected by Statistics Norway using telephone interviews. We validate the agreement between the individual- and occupational-based mechanical exposure index (MJEI) estimates using Spearman`s Rho, sensitivity and specificity measures. The predictive validity of the mechanical job exposure matrix was tested investigating the association between individual reported lower back pain and long-term sick absence and the individual- and MJEI estimates. Furthermore, we investigate the association between disability benefits, mortality and the number of long-term sick absence periods, retrieved from register data, and the occupational-based mechanical exposure (MJEI) estimates. Results: The analysis shows a fair-to-moderate overlap between occupational-based mechanical exposure index (MJEI) and the index based on individual reported exposures. When assessing the predictive value of the occupational-based mechanical exposure index to the index based on the individual reported exposures, the MJEI showed lower and reproducible associations with lower back pain for both men and women. For long-term sick leave, the MJEI showed higher and reproducible associations for both genders. As for the register-based outcomes, the MJEI predicts disability and a significant higher number of long-term sickness benefits periods for both men and women. For men the MJEI also predicts higher mortality. Conclusion: The predictive value of the mechanical job exposure index (MJEI) is overall acceptable and will be useful in register-based studies lacking information on these types of exposures.