Asbestos Exposure Data is Reviewed and Categorized

The analysis presented here focuses on occupational respiratory conditions potentially related to asbestos exposure: lung cancer, asbestosis, and other nonmalignant respiratory disease. Mesothelioma was not coded as a distinct cause of death under ICD coding rubrics until 1999, so the SMR for mesothelioma is based on only 3 years of data (1999–2001).

Cumulative exposure data were categorized to achieve an approximately equal number of cases in each exposure category, a method previously found to be most efficient, while maintaining sufficient person-years in each exposure category to obtain valid estimators.

Person-years at risk and observed deaths were accrued from the date comparison rates were available (1 January 1960), or from the date of first exposure (if later) until the time that each worker died or was lost to follow-up, or until the end of the study (31 December 2001).

Ten workers lost to follow-up were considered to be alive, but person-years of observation were truncated on the date each of these workers was last observed alive (date of termination, or last date known to be alive in earlier vital status follow-up).

One worker was excluded from the SMR analysis because he died in Canada; another was excluded because his date of death was unknown. Twenty-four workers known to have died, but with cause of death unknown, were added to the residual cause code (NIOSH 2001).