American Journal of Epidemiology Vol. 142, No. 3: 353-362
Copyright © 1995 by The Johns Hopkins University School of Hygiene and Public Health
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Cost-Efficient Design of a Diet Validation Study
1Department of Preventive Medicine, School of Medicine, University of Southern California Los Angeles, CA.
2Department of Epidemiology, UCLA School of Public Health Los Angeles, CA.
3Epidemiology Program, Cancer Research Center, University of Hawaii Honolulu, HI.
Reprint requests to Dr. Daniel Stram, Department of Preventive Medicine, School of Medicine, University of Southern California, Center for the Health Professions, CHP-2201, Los Angeles, CA 90033-9987.
Validation studies of food frequency questionnaires (FFQs) describe the extent to which the FFQ reflects true diet and the relation between measured and true diet (calibration). Calibration data can be used to estimate the relation between disease and diet that would have been observed in the absence of error due to the FFQ. In this paper, the authors consider the optimal design of a validation study when the goal is precise calibration of an FFQ. The authors posed the following question: Under the constraint of a fixed total cost for a validation study, what is the optimal choice of number of subjects (n) and number of days (m) of diet records (or 24-hour recalls) per subject? The optimal n and m were found to depend upon 1) the ratio between the costs of the initial and subsequent 1 -day diet records and 2) the ratio of the variance in day-to-day nutrient intake to the variance in true diet for a fixed FFQ value. Data for the two ratios and optimal values of n and m are given under a variety of realistic scenarios. The authors conclude that in most settings the optimal study design will rarely require more than four or five 1-day diet records per subject.
diet surveys; epidemiologic methods; questionnaires; statistics
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