Table 1.

Checklist for the assessment of quality

Study design	1. Positive if the study was a cohort study or a case–control study as opposed to cross-sectional studies
	2. Positive if the studied age group was relevant for COPD
Exposure assessment	3. Positive if exposure assessment happened independently of outcome, for example, through an expert- rated JEM, job title or register data
Exposure-response information	4. Positive if level and/or duration of exposure was assessed
Outcome assessment	5. Positive if COPD was diagnosed by a physician, by spirometry or by death registered on death certificates
Confounding	6. Positive if the analyses were adjusted for the potential confounders: smoking, age and sexa either in stratified or multivariate analysis

^aWhere both sexes were included in analyses.