Application of Standardized Proportional Mortality Ratio to the Assessment of Health Risk in Relatively Healthy Populations: Using a Study of Cancer Risk in Telecommunication Workers with Excess Exposure to Acid Mists as an Example.

Ying-Fong Ker,How-Ran Guo,Perng-Jy Tsai

doi:10.3390/ijerph18189870

Abstract

When a study population is relatively healthy, such as an occupational population, epidemiological studies are likely to underestimate risk. We used a case study on the cancer risk of workers with exposure to acid mists, a well-documented carcinogen, to demonstrate that using proportional mortality ratios (PMRs) is more appropriate than mortality ratios in assessing risk in terms of mortality. The study included 10,229 employees of a telecommunication company who worked in buildings with battery rooms. In these buildings, the battery rooms had the highest levels of sulfuric acid in the air (geometric mean = 10.7 μg/m3). With the general population in Taiwan as a reference, a decreased standardized mortality ratio (0.42, p < 0.01) from all causes combined, between 1 January 1985 and 31 December 1996, was observed, indicating a healthy worker effect. When we reanalyzed the data using standardized PMR, elevated risks were observed for all cancers combined (1.46, p = 0.01) and cancers of the digestive organs and peritoneum (1.61, p = 0.02), especially stomach cancer (2.94, p = 0.01). The results showed that PMR can detect increases in mortality when a study population is generally healthier than the comparison population and call for further studies on the possible carcinogenic effects of low-level acid mist exposures on the stomach.

Highlights

In epidemiological studies, when the study population is relatively healthier than the comparison population, risk is likely to be underestimated
When a study evaluates effects of a health hazard using mortality as the indicator of outcome, if an occupational population with exposure to that health hazard is compared to the general population, the risk associated with the health hazard is likely to be underestimated
The study population consisted of employees of a large telecommunication company in Taiwan, who had worked in buildings with battery rooms

Summary

Introduction

In epidemiological studies, when the study population is relatively healthier than the comparison population, risk is likely to be underestimated. When a study evaluates effects of a health hazard using mortality as the indicator of outcome, if an occupational population with exposure to that health hazard is compared to the general population, the risk associated with the health hazard is likely to be underestimated. This phenomenon is often called the “healthy worker effect” [1]. With the general population as the standard, the SMR for a study population that is relatively healthier (such as an occupational population) will underestimate the mortality experience of the study population, because the baseline mortality risk is initially lower than that of the standard population.

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Discussion

Conclusion