Chlorinated drinking water and bladder cancer: effect of misclassification on risk estimates.
Data are presented from the Iowa portion of the National Bladder Cancer Case-Control Study demonstrating the effect of misclassification on depressing odds ratio estimates for years of exposure to chlorinated drinking water and bladder cancer. Four methods (METHODS 1 through 4) of quantifying chlorination exposure with sequentially decreasing degrees of misclassification are presented for the 268 bladder cancer cases and 658 population-based controls fulfilling criteria for inclusion in this study. Twenty-eight other risk factors for bladder cancer were considered along with chlorinated drinking water exposure estimated by METHOD 4. Stepwise regression models included as significant factors cigarette smoking (p less than .001), chlorination exposure (p = .038), and irradiation to the pelvic area (p = .040). Replacement of chlorinated drinking water exposure estimated by METHOD 4 with any of the remaining three methods resulted in models that included cigarette smoking and irradiation to the pelvic area, but not chlorination exposure. Thus, misclassification of chlorination exposure signified the difference between observing and not observing an association with bladder cancer.
Department of Preventive Medicine and Environmental Health, University of Iowa, Iowa City.
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Lynch
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Woolson
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O'Gorman
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Cantor
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002713:Chlorine / Q000009:adverse effects*; D002965:Classification; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D007484:Iowa; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects; D013997:Time Factors; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced* / Q000453:epidemiology; D014881:Water Supply
D002713:Chlorine