In Nordic countries, national register data have been a valuable source of information for research for decades. They have even been dubbed “a goldmine” for research (1) as they include longitudinal data on the entire national populations, characterized by numerous variables and covering a wide range of life domains. However, one limitation is the lack of information on working conditions. To remedy this shortcoming, scholars have constructed job exposure matrices (JEMs) to create information on work environments, not for individuals, but for job titles (2). With a history dating back to the 1980s, JEMs have proven useful in research on data where such information is missing (3, 4). The JEM method is cost-effective; it provides systematic, unbiased, and reproducible results, and renders objective job-related information on exposures, in contrast to the subjective information given by respondents in surveys (3). However, this approach is not without its challenges and pitfalls. One major problem with a JEM is that it entails the risk of misclassification, which may limit its applicability. This relates to the exact definition of exposures, as well as the classification of exposed or non-exposed. Job exposure matrices do not take into account the variation in working tasks and activities or differences in working locations over time or between workers with the same job titles (3, 5).
This raises questions about the reliability and validity of specific JEMs. This article investigated the statistical properties of a Job Strain Index (JSI) and its dimensions and components, based on Karasek’s Demand-Control Model (6). The paper built on innovative work undertaken by Hanvold et al. (2019), but exploited survey data with a much larger number of observations and, in addition, used register data. Hence, our study moved beyond Hanvold et al. by obtaining higher precision in the survey estimates, as well as benefitting from test results from a different and independent data source, register data.
Previous Research
A substantial number of current studies have constructed and evaluated the reliability and validity of a psychosocial JEM. The reliability of the JEM was mainly reported by indicators, such as the internal consistency of the constructed JEM, kappa statistics to test the agreement between individual-based and occupational-based job exposure, and sensitivity and specificity to report the ability of constructed JEM to identify the exposure or non-exposure individuals, respectively. Psychosocial exposures at work are mostly described by the dimensions of Karasek’s models, including job demand and job control, which were commonly reported to have satisfactory internal consistency (7, 8). A validation of alternative formulations of job strain supported using a continuous index when investigating health outcomes instead of the more common quadrant approach based on dichotomies, which inevitably will lead to loss of information (9). The performance of the constructed psychosocial JEM varied across countries, which was reported as good for both job demand and job control in Australia (10), low for job control and bad for job demands in France (11), and good for job control and job strain in Finland (12). The accuracy of detecting job exposure has been reported differently between genders (11, 12), but mostly suggests that the ability to identify psychosocial job exposure is better for women than for men. The reliability of the JEM was found to be different among exposures, which is likely to be higher for job control and job strain than for job demand (13).
The validity of the constructed JEM was tested by evaluating criterion-related validity using large population data. Based on solid evidence about possible links between psychosocial work exposures, especially high job strain (high job demand and low job control), and the risks of ill health, i.e., sickness absence (14), disability pension (15), and cardiovascular diseases (16) and different mental disorders (17; 18), such as risk for depressive symptoms (19, 20) and sleeping problems (21, 22), various health outcomes were taken into account to examine the reproducible likelihood of the constructed JEM compared with individual-based job exposure and the predictive validity of the JEM based on register data. The assessment of psychosocial work factors measured by JEM can also help to answer the question of whether the relationship between exposure and outcome is consistent regardless of the method used (16).
Recent Scandinavian studies have constructed and validated the JEM based on Karasek’s Demand-Control Model (1979), using large population data, such as the Danish JEM based on Work Environment Cohort Study data, including all patients aged 18–65 who received depressive and anxiety disorder treatments (23), the Swedish JEM using a large study population of all individuals aged 30–54 (24), the Finnish JEM utilizing the Health 2000 Study, and the Finnish National Work and Health Surveys (12). The results showed the ability of a constructed JEM to predict various health outcomes, i.e., anxiety disorders (23), depression (12), sickness absence, and disability pension (24), with different patterns between men and women.
With respect to the context of Norway, a previous study by Hanvold et al. (2019) utilized data of the work environment in 2006 and 2009 to construct group-based exposure estimations and to assess psychosocial JEM performance. The constructed JEM showed fair to poor agreement with the different performances between genders, reported to be higher among women than men (4). The constructed JEM in Hanvold et al.’s study showed a good ability to identify occupations that are exposed to job strain, job control, and job demand. However, this study only investigated the concurrent validity of psychosocial occupational-level job exposure on low back pain.
This study used five waves of the nationwide Norway Survey of Living Conditions in the Work Environment. This pooled dataset was used to examine four aspects of reliability (i.e., agreement, consistency, sensitivity, and specificity) associated with the JSI and its dimensions and components. Survey data were further used to assess the construct validity by means of factor analysis and the concurrent validity of the JSI, based on both individual and occupation exposures, using individually reported “long term sick leave”, “anxious symptoms”, “depressive symptoms” and “sleeping difficulty symptoms” as health outcomes. Finally, we assessed the predictive validity of the JSI for the entire working-age population in Norway, using register data and “disability benefits”, “mortality”, and “number of long-term sick absence periods” as health indicators. Where appropriate, the analyses were stratified by gender, as current research has shown divergent effects of work stressors on men and women (18).