It is well known that in a working population the risk for diseases of the circulatory system is lower due to the "healthy worker effect", and therefore, in a proportionate mortality study the other causes could be artificially increased.
"Where the plant management, in order to meet the necessity of replacing men by women, has rearranged or lightened the job, perhaps with the employment of helpers to do heavy lifting or the like, a study of job content and job evaluation should afford the basis for setting 'proportionate rates for proportionate work.'".
We performed a separate meta-analysis for proportionate mortality studies.
Proportionate mortality studies (PMR) were excluded (n = 12 [ 27– 38]) as their results depend on the proportions of death from different causes [ 39].
Although the results of 13 proportionate mortality studies were not included in the combined analysis, they also demonstrated a significantly increased risk of lung cancer in painters (meta-PMR, 1.22; 95% CI, 1.17 1.28).
Proportionate mortality studies, which compare the percentage of all deaths from a specified cause between an exposed group of interest and an unexposed or general population group, can give rise to misleading conclusions about risk associations if they are used to compare groups with different distributions of causes of death unrelated to the exposure under study.
This study employed proportionate stratified sampling in selecting the sample.
The choice of study sites, proportionate allocation of study population and recruitments of participants was by convenient sampling, however, this does not invalidates the research findings.
Then, the 9000 respondents were distributed to the study kebeles proportionate to the population size.
Cases were selected from the study sites proportionate to the number of cases seen at the site in 2009.
