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

Authors

  • S.R. Silver MA,

    Corresponding author
    1. Division of Surveillance, Hazard Evaluations, and Field Studies, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, MS R-44, Cincinnati, Ohio
    • Division of Surveillance, National Institute for Occupational Safety and Health, Hazard Evaluations and Field Studies, 4676 Columbia Parkway, MS R-44, Cincinnati, OH 45226.
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  • R.A. Rinsky PhD,

    1. Division of Surveillance, Hazard Evaluations, and Field Studies, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, MS R-44, Cincinnati, Ohio
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  • S.P. Cooper PhD,

    1. Texas A & M School of Rural Public Health, 3000 Briarcrest Drive, Suite 300, Bryan, Texas
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  • R.W. Hornung DrPH,

    1. Institute for Health Policy and Health Services Research, University of Cincinnati Medical Center, P.O. Box 670840, Cincinnati Ohio
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  • D. Lai PhD

    1. School of Public Health, University of Texas Health Science Center at Houston, P.O. Box 20186, Houston, Texas
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  • Work was performed at National Institute for Occupational Safety and Health.

    Mention of company names or products does not constitute endorsement by the National Institute for Occupational Safety and Health.

  • This article is a US Government work and, as such, is in the public domain in the United States of America.

Abstract

Background

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.

Materials and Methods

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.

Results

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.

Conclusions

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. Am. J. Ind. Med. 42:481–489, 2002. Published 2002 Wiley-Liss, Inc.

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