EXPOSURE MISCLASSIFICATION DUE TO RESIDENTIAL-MOBILITY DURING PREGNANCY IN EPIDEMIOLOGIC INVESTIGATIONS OF CONGENITAL-MALFORMATIONS

This study addressed the question of how maternal migration between co nception and birth affects estimates of risk in studies of congenital malformations when movement is related to the exposure. For example, i n studying the potential association between proximity to a chemical w aste site and the occurrence of birth defects, incorrect inferences mi ght be drawn if maternal residence at birth was used as a surrogate fo r exposure at conception in the case when a significant amount of medi a attention influenced some women to move away from the site after bec oming pregnant. A simple statistical model is proposed that defines th e distance to a fixed exposure point measured at birth as a function o f the distance to the point measured at conception, the probability of movement, the direction of movement, and the distance moved. Bias is the difference between the expected results when distance is measured at birth versus conception. The amount of bias can be substantial for movement patterns that may be likely to occur. This simplified model w as used in an effort to explore and better understand the relationship s between maternal migration and risk.