Measurement of exposure to nutrients: an approach to the selection of informative foods.

Frequently, epidemiologic questionnaires are designed to measure several individual level exposures, including exposure to one or more nutrients. Although most nutrients are contained in a large number of foods, constraints on questionnaire length permit the inclusion of only a subset of these. In this paper, the authors review the two common methods of food selection, and they propose two new methods. When the intent is to estimate the effect of the nutrient on disease risk using a logistic regression model, the authors show that their Max_r method is optimal. With the use of case-control data, they examine the assumption of non-differential measurement error that is essential to the validity of all analyses that rely on shortened questionnaires. They conclude by combining the statistical considerations developed for judging adequacy of a selection method with their empirical results and suggest new goals for dietary questionnaires and a new approach to questionnaire construction consistent with those goals.