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Methodology
Impact of pesticide exposure misclassification on estimates of relative risks in the Agricultural Health Study
  1. Aaron Blair1,2,
  2. Kent Thomas3,
  3. Joseph Coble4,
  4. Dale P Sandler5,
  5. Cynthia J Hines6,
  6. Charles F Lynch7,
  7. Charles Knott8,
  8. Mark P Purdue1,
  9. Shelia Hoar Zahm1,
  10. Michael C R Alavanja1,
  11. Mustafa Dosemeci1,
  12. Freya Kamel5,
  13. Jane A Hoppin5,
  14. Laura Beane Freeman1,
  15. Jay H Lubin1
  1. 1Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland, USA
  2. 2National Cancer Institute, Bethesda, Maryland, USA
  3. 3National Exposure Research Laboratory, US Environmental Protection Agency, Research Triangle Park, North Carolina, USA
  4. 4Annapolis, Maryland, USA
  5. 5Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
  6. 6Division of Surveillance, Hazard Evaluation, and Field Studies, National Institute for Occupational Safety and Health, Cincinnati, Ohio, USA
  7. 7Department of Epidemiology, University of Iowa, Iowa City, Iowa, USA
  8. 8Centers for Public Health Research and Evaluation, Battelle, Inc., Research Triangle Park, North Carolina, USA
  1. Correspondence to Aaron Blair, National Cancer Institute, Executive Plaza South, Room 8008, Bethesda, MD 20892, USA; blaira{at}mail.nih.gov

Abstract

Background The Agricultural Health Study (AHS) is a prospective study of licensed pesticide applicators and their spouses in Iowa and North Carolina. We evaluate the impact of occupational pesticide exposure misclassification on relative risks using data from the cohort and the AHS Pesticide Exposure Study (AHS/PES).

Methods We assessed the impact of exposure misclassification on relative risks using the range of correlation coefficients observed between measured post-application urinary levels of 2,4-dichlorophenoxyacetic acid (2,4-D) and a chlorpyrifos metabolite and exposure estimates based on an algorithm from 83 AHS pesticide applications.

Results Correlations between urinary levels of 2,4-D and a chlorpyrifos metabolite and algorithm estimated intensity scores were about 0.4 for 2,4-D (n=64), 0.8 for liquid chlorpyrifos (n=4) and 0.6 for granular chlorpyrifos (n=12). Correlations of urinary levels with kilograms of active ingredient used, duration of application, or number of acres treated were lower and ranged from −0.36 to 0.19. These findings indicate that a priori expert-derived algorithm scores were more closely related to measured urinary levels than individual exposure determinants evaluated here. Estimates of potential bias in relative risks based on the correlations from the AHS/PES indicate that non-differential misclassification of exposure using the algorithm would bias estimates towards the null, but less than that from individual exposure determinants.

Conclusions Although correlations between algorithm scores and urinary levels were quite good (ie, correlations between 0.4 and 0.8), exposure misclassification would still bias relative risk estimates in the AHS towards the null and diminish study power.

  • Epidemiology
  • exposure assessment
  • retrospective exposure assessment
  • agriculture
  • pesticides

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Footnotes

  • Mention of trade names or commercial products does not constitute endorsement or recommendation for use. This article has been subjected to Agency administrative review and approved for publication.

  • The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the National Cancer Institute, National Institute of Environmental Health Sciences, U.S. Environmental Protection Agency or National Institute for Occupational Safety and Health.

  • Funding This research was partially supported by the Intramural Research Program of the NIH (Division of Cancer Epidemiology and Genetics, National Cancer Institute (Z01CP010119) and the National Institute of Environmental Health Sciences (Z01-ES049030-1)). This work has been funded in part by the U.S. Environmental Protection Agency under Contracts 68-D99-011 and 68-D99-012, and through Interagency Agreement DW-75-93912801-0.

  • Competing interests None.

  • Ethics approval This study was approved by the National Institutes of Health Special Studies Institutional Review Board, protocol number OH93-NC-N013, and also by Institutional Review Boards at the University of Iowa, Westat, Inc., RTI International and Battelle, Inc.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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