THE DUTCH EPIC FOOD FREQUENCY QUESTIONNAIRE .1. DESCRIPTION OF THE QUESTIONNAIRE, AND RELATIVE VALIDITY AND REPRODUCIBILITY FOR FOOD GROUPS

Background. A self-administered food frequency questionnaire was devel oped for the Dutch cohort of the European Prospective Investigation in to Cancer and Nutrition (EPIC). Habitual consumption of 178 food items can be calculated from the questionnaire data. Methods. Reproducibili ty and relative validity for food group intake were investigated in a population of 121 Dutch men and women. The questionnaire was administe red three times at 6-month intervals in order to determine the reprodu cibility. To assess the relative validity 12 monthly 24-hour recalls s erved as the reference method. Results. Spearman rank order correlatio n coefficients between estimates of food group intake assessed by repe ated questionnaires ranged from 0.45 to 0.92. For men, Spearman correl ation coefficients between estimates of food group intake based on the questionnaire and those based on 24-hour recalls ranged from 0.21 for cooked vegetables to 0.78 for sugar and sweet products, with a range of 0.61, For women the median was 0.53, with a minimum of 0.31 for veg etables and a maximum of 0.87 for alcoholic beverages. The photographs in the questionnaire for the estimation of portion sizes contributed little to the relative validity of the ranking of subjects, However, o n the group level most median food group estimates based on photograph ic portion sizes were closer to the median intakes as assessed by 24-h our recalls than those based on standard portion sizes. Conclusions. T he questionnaire seems adequate for ranking Dutch EPIC subjects accord ing to intake of most food groups, although the relative validity for some food groups, such as vegetables and fish, remains of concern.