Sunday, January 23, 2005

Get Rich or Die (sooner)

Identification of employment related hazards through mortality studies among workers often hinges on interpretation of the healthy worker effect (HWE). Hourly workers who achieve enough job tenure to get into cohort studies typically enjoy improved mortality experience compared to the general population, yet suffer increased mortality compared to professional and white collar workers in the same industry. African American workers typically show a larger HWE than whites, yet suffer increased mortality compared to white workers in the same enterprise.

The study cited below provides information on that general population to assist interpreting occupational cohort studies.

The investigators calculated mortality differences by socioeconomic status (SES). SES was determined according to the "usual occupation" listed on their death certificates, and were divided into 4 groups. For all-cause mortality, rate ratios from lowest to highest SES quartile for men and women were 2.02, 1.69, 1.25, and 1.00 and 1.29, 1.01, 1.07, and 1.00, respectively. Higher status people were strongly protected from most major causes of death except breast cancer and colorectal cancer. The investigators concluded that mortality differences by SES were sustained through the 1990s and are increasing for men.

BrooklynDodger notes the important public health lesson of this study is the great benefit – nearly two fold - of being in the highest class, compared to the lowest. Class distinction exacts a cost in years of life. Few studies of this type are done and published, perhaps because of their political implications. This study ended observation in 1997. It would be of great value to update this study. The investigators note that these mortality differences are not fully explained by known differences in prevalence of health risk factors by class.

BrooklynDodger thinks this data demands that any occupational cohort mortality study at the minumum stratify on salaried vs. hourly.

For interpretation of occupational cohort mortality studies BrooklynDodger wishes the investigators had devoted more effort to people not usually employed. The investigators observed that 7% of men were not classifiable - unemployed, military, students, volunteers, etc. There are likely additional people who are not usually employed, or on long term disability but whose occupation is noted on death certificate. This 7% might be expected to have even less favorable mortality experience than those who achieved an SES classification in this study. Further, BrooklynDodger expects that persons in lower SES job classification in this study are richer in the marginally employed, persons in the general population but not in occupational cohorts.

All-cause and cause-specific mortality by socioeconomic status among employed persons in 27 US states, 1984-1997.

Am J Public Health. 2004 Jun;94(6):1037-42.

Steenland K, Hu S, Walker J.Department of Environmental and Occupational Health, Rollins School of Public Health, 1518 Clifton Avenue, Atlanta, GA 30322, USA.

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