Exposure assessment error and its handling in nutritional epidemiology.

Exposure assessment is the weakest element in nutritional epidemiologic studies. In the absence of an adequate arsenal of biomarkers of intake in the United States, food frequency questionnaires are widely used to assess habitual frequency of consumption of foods. These tools need to be designed for the population under study, based on prior information on the eating behavior of the population. The questions to be addressed to insure appropriate application of these tools are presented. The influence of various sources and types of measurement error on various scientific hypotheses is addressed. In assessment of nutrient adequacy, information on intra- to interindividual variation of the nutrient or substance of interest is essential. Risk assessment requires examination of sources and extent of bias and differential and nondifferential measurement error within the study. The theory required for error correction is well developed, but rarely carried out because of lack of software and lack of information needed to calibrate the measures.