Estimating the Relation between Dietary Intake Obtained from a Food Frequency Questionnaire and True Average Intake

Abstract

Knowledge of the regression reiaticm between dietary intake reported on a food frequency questionnaire and true average intake is useful in interpreting resutts from nutritional epidemiologic studies and in planning such studies. Studies which validate a questionmire against a food record may be used to estimate this regression relation provided the food record is compkted by each subject on at least two occasions. Using data collected from women aged 45–69 years during 1985–1 986 in the pilot study of the Women's Health Trial, the authors show how variation in diet over time and intralndividual correlation between a questionnaire and food r m d obtained dose ogether in time affects the estimatim of the regression. The authors' method provides estimates of the regression slope and the questionnaire ‘bias’ that are corrected for hese effects, together with standard m. A computer program in the SAS language, for carrying out the analysis, is provided. Am J Epidemiol 1991 ;134;310–20.