Impact of pesticide exposure misclassification on estimates of relative risks in the Agricultural Health Study.
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.
National Cancer Institute, Executive Plaza South, Room 8008, Bethesda, MD 20892, USA. blaira@mail.nih.gov
Aaron
A
Blair
Kent
K
Thomas
Joseph
J
Coble
Dale P
DP
Sandler
Cynthia J
CJ
Hines
Charles F
CF
Lynch
Charles
C
Knott
Mark P
MP
Purdue
Shelia Hoar
SH
Zahm
Michael C R
MC
Alavanja
Mustafa
M
Dosemeci
Freya
F
Kamel
Jane A
JA
Hoppin
Laura Beane
LB
Freeman
Jay H
JH
Lubin
D015084:2,4-Dichlorophenoxyacetic Acid / Q000652:urine; D000383:Agriculture / Q000706:statistics & numerical data*; D000465:Algorithms; D015415:Biomarkers / Q000652:urine; D004784:Environmental Monitoring / Q000379:methods; D006801:Humans; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis* / Q000706:statistics & numerical data; D010575:Pesticides / Q000633:toxicity*; D011446:Prospective Studies; D011728:Pyridones / Q000652:urine; D018570:Risk Assessment / Q000379:methods
D015415:Biomarkers; D010575:Pesticides; D011728:Pyridones; D015084:2,4-Dichlorophenoxyacetic Acid; C012587:3,5,6-trichloro-2-pyridinol
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