Measuring length of exposure to fluoridated water

Previous studies have measured subjects' exposure to fluoridated water in two ways: number of years exposed to fluoridation and a dummy variable indicating the fluoridation status of the subjects' present community. The former assumes that fluoride concentrations of water supplies are constant across years, while the latter assumes subjects have never changed residences. Measurement error may occur when either assumption is not satisfied. These two sources of error may be reduced in a newly developed measure of lifetime fluoridation exposure (LFE) containing residence history and fluoride level elements. The aim of this paper is to examine the accuracy of the three measures. Results reveal that the number of years measure and LFE are highly correlated (0.98) and have similar effects in a regression model, indicating both are valid measures of fluoridation exposure. LFE also appears to be fairly insensitive to measurement error due to inaccurate recall of residence histories. Measuring fluoridation exposure with a dummy variable is not recommended.