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2973651 
Journal Article 
Assessment of the Working Lifetime Risk of Exposure in an Occupational Cohort 
Walter, SD 
1989 
Yes 
American Journal of Epidemiology
ISSN: 0002-9262
EISSN: 1476-6256 
NIOSH/00185629 
129 
1 
230-231 
In this letter, potential errors were identified in the method of risk assessment proposed by the International Agency for Research on Cancer (IARC) in estimating the expected number of excess leukemia cases in an occupational cohort exposed to benzene (71432) throughout their working lives. As proposed, the method attempted to extrapolate from the duration of employment of the cases diagnosed in the early years of follow up to the expected number of cases occurring over an entire working lifetime under continual exposure. In this method, one of the factors considered was the average duration of exposure for leukemia cases diagnosed to date. The author agrees with earlier critics that the lifetime risk projections using the early mortality experience of a cohort should involve as numerators the distribution of exposure duration from the entire cohort, not just the cases.