Our results support the finding that psychosocial working conditions have a confounding effect, based on the small but decisive changes in the effects of occupational groups on the risk of DP when taking into account psychosocial working conditions.
Considering the practical working environment of occupational groups in the intervention sites, assistance of occupational/community leaders was essential for getting workers as participants in the study.
Epidemiological studies of occupational groups are often confounded by a 'healthy worker effect', that is, a reduced overall risk estimate compared with the general population.
Hospital-based health promotion programs could take the differences of occupational groups into consideration to tailor programs to the needs of different occupational groups.
Although occupational exposures to dusts and fumes have been shown to contribute greatly to the burden of chronic obstructive pulmonary disease (COPD) (Balmes et al. 2003; Christiani 2005; Hnizdo et al. 2002; Meldrum et al. 2005; Trupin et al. 2003), previous studies have had limited ability to examine the health effects of a specific occupational group or exposure.
This result is different from another recent study that analyzed the effects of occupational licensing for 13 universally licensed occupations (not including opticians) and found that the largest wage premiums of occupational licensing materialized after 10 years.
In order to investigate the independent effect of sector-defined occupational group, psychosocial working conditions and job strain, we further adjusted the models for the potential confounders found to be significant in the separate analyses, including children living at home, marital status, educational level and type of living area.
His group's research in applied micro-economic theory focuses on: supply-side issues in higher education, the effects of occupational licensing on labor market discrimination, and the link between residential segregation and educational outcomes.
