LIMITATIONS
death, asthma, COPD
COPD, ASTHMA
The occupational classifications for the 1996 study cohort were done from the postal questionnaire answers and reflect the way the occupations were understood in the mid-1990s (NYK and SEI coding). The original codes were done with the given occupational titles and may not always reflect on actual working conditions as occupations within the same title can vary. We used the JEM to assess a figure for airborne occupational exposure based on the main occupation title of the participant coded into ISCO-88. The original JEM used only three types of exposure (biological, mineral dust, and gas/fumes). These were then used to define none (no exposure in any group), intermediate (intermediate exposure in any group), and strong (strong exposure in any group) exposure groups. Specific named irritants and types of chemicals were not considered in the JEM, nor any measurements results were available, and the assignment of the tiers of exposure was not done at a specific level. Although the JEM would have allowed us to observe three different qualities of exposure, a decision was made to gather the three different exposures together as shown in Supplementary Table 3, The exposure estimation was based on the main occupation at 1996 or earlier. Table As for the validity of the questions, the question on physician-diagnosed asthma has earlier been reported to have high specificity (94%) in a Swedish study,In this study, the prevalence of the coexisting diagnosis in 1996 varied approximately 1% to 2% in males, and the high occupational exposure group has the highest prevalence. It is possible that this might have given some bias in our results as well, with the milder cases of both asthma and COPD being left undiagnosed and therefore strengthening the findings for the differences in mortality. For example, the overall COPD prevalence in a systematic worldwide review conducted in 2006 gave a 7% prevalence of COPDAlthough we looked at the whole group of respiratory mortality causes of death, it is possible that there has been some amount of underreporting of COPD in the cause of death diagnose codes as has been previously seen in Sweden,