Measurement error correction in nutritional epidemiology based on individual foods, with application to the relation of diet to breast cancer

Nutrient intake is often measured with error by commonly used dietary instr uments such as the food frequency questionnaire (FFQ) or 24-hour recall. Mo re accurate assessments of true intake are obtained by using weighed diet r ecords, in which subjects record what they eat on a real-time basis, but th ese records are expensive to administer. Validation studies are often perfo rmed to relate "gold standard" intake to intake according to surrogate inst ruments and to correct relative risk estimates obtained in the main study f or measurement error. Most measurement error correction methods use validat ion study data at the nutrient level. However, subjects almost always repor t intake at the food rather than the nutrient level. In addition, the valid ity of measurement of different foods can vary considerably; it is relative ly high for some foods (e.g., beverages) but relatively low for others (e.g ., meats, vegetables). This differential validity could be incorporated int o measurement error methods and potentially improve on nutrient-based measu rement error methods. In this paper, the authors discuss correction methods for food-based measurement error and apply them to study the relation betw een FFQ intake in 1980 and incident breast cancer in 1980-1994 among approx imately 89,000 women in the Nurses' Health Study, in whom approximately 3,0 00 incident breast cancers were observed.