Effect of follow-up time on risk estimates: a longitudinal examination of the relative risks of leukemia and multiple myeloma in a rubber hydrochloride cohort.
Silver-SR; Rinsky-RA; Cooper-SP; Hornung-RW; Lai-D
Am J Ind Med 2002 Dec; 42(6):481-489
Choice of follow-up time for an occupational cohort can influence risk estimates. We examined the effects of follow-up time on relative risk estimates for leukemia and multiple myeloma in a cohort of 1,845 rubber hydrochloride workers. We generated standardized mortality ratios (SMRs) for yearly follow-ups, beginning each study in 1940 and increasing study end dates from 1950 through 1996. We used Cox proportional hazards modeling to explore the effects of follow-up time on the exposure-response relationship. The SMR for leukemia rose to 13.55 in 1961 and fell nearly monotonically to 2.47 by 1996. Cox modeling suggested interaction between cumulative exposure and time since exposure. A longer time to peak risk was seen for multiple myeloma. Because summary risk estimates change with follow-up time, exposure limits set using these estimates may not adequately protect workers. Consideration of appropriate follow-up time and use of more complex temporal models are critical to the risk assessment process.
Risk-analysis; Risk-factors; Rubber-workers; Benzenes; Epidemiology; Leukemogenesis; Worker-health; Workplace-monitoring; Occupational-exposure; Mortality-data; Mortality-rates
National Institute for Occupational Safety and Health, Division of Surveillance, Hazard Evaluations and Field Studies,4676 Columbia Parkway,MS R-44, Cincinnati,OH 45226, USA
American Journal of Industrial Medicine