Background: Recent studies in childhood cancer suggest that maternal vitamin supplementation may reduce the risk of leukemia, neuroblastoma, and certain types of childhood brain tumors. For example, Ross et al. (Cancer 2005;104:405-10) found a significantly reduced risk of acute lymphoblastic leukemia (ALL) but not acute myeloid leukemia (AML) in children with Down syndrome whose mothers reported any vitamin supplement use prior to knowledge of pregnancy (ALL odds ratio (OR) adjusted for confounders = 0.51, 95% confidence limits (CL): 0.30, 0.89; AML OR adjusted for confounders = 0.92, 95% CL: 0.48, 1.76). Recall of exposures, including maternal vitamin supplement use, however, may be difficult and subject to error. Epidemiologists are encouraged to quantitatively adjust for systematic error in study results, but often do not.
Methods: We quantified the impact that misclassification of maternal vitamin supplement use may have had on the observed ORs in this study. We used uncertainty analysis to calculate ORs adjusted for inaccurate reporting of vitamin supplement use under assumed probability distributions for exposure misclassification parameters.
Results: Given our assumptions, adjustment for exposure misclassification yielded ORs that were predominantly more protective for ALL than the unadjusted OR.
Conclusions: Uncertainty analysis can give important insights into the magnitude and direction of error in study results due to exposure misclassification.
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