To proxy this within-occupational task heterogeneity, we rely on the relevance of the typical worker in each occupation, where the 'typical worker' is defined as a worker who employs the most common way of performing an occupation.
Second, there is heterogeneity in occupational cohort studies with regard to industry, sample size, documentation and level of benzene exposure, and documentation of the percentage of a given cohort that had true, nontrivial exposure to benzene.
We developed three different quality dimensions that reflect the substantial changes in diagnosis and categorization of lymphoid neoplasms over the last half century and the heterogeneity in occupational cohort studies with regard to industry, sample size, and documentation of benzene exposure.
Given the changing nature of the diagnosis of lymphoid neoplasms over time and the heterogeneity of occupational benzene cohort study quality in the literature, it is a challenge to discern the nature of the relationship between benzene and lymphoid neoplasms.
In subgroup analysis (subgroups were defined by the type of study and by population, that is, occupationally and environmentally exposed adults and children), there was no heterogeneity between occupational studies (I = 0), between the studies of environmentally exposed children (I = 0), and moderate heterogeneity among the studies of environmentally exposed adults (I = 55.2%).
Heterogeneity regarding exposure within occupational categories implies that occupation, as an explanatory variable, does not capture all effects of occupational exposures on tinnitus.
Second, because of a lack of data we could not do stratified analysis by unit or department, although such an analysis could have given more insight into the consequences on absenteeism rates of heterogeneity in potential occupational exposures to influenza.
Nevertheless, recruitment from diverse neighbourhoods and settings allowed for a sample with reasonable heterogeneity in age, occupational status and ethnic backgrounds and made it possible to stratify the analyses by sociodemographic characteristics.
Heterogeneity regarding noise and other exposure within occupational categories implies that occupation, as an explanatory variable, does not capture all effects of occupational exposures on tinnitus.
In the occupational studies, there is likely considerable heterogeneity of exposures to professional drivers (46), as well as to filling station (47), aluminum industry (52), welding (54), mint (53), and battery workers (45).
