Background: A self-administered food frequency questionnaire was developed for the Dutch cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). Habitual consumption of 178 food items can be calculated from the questionnaire data.
Methods: Reproducibility and relative validity for food group intake were investigated in a population of 121 Dutch men and Women. The questionnaire was administered three times at 6-month intervals in order to determine the reproducibility. To assess the relative validity 12 monthly 24-hour recalls served as the reference method.
Results: Spearman rank order correlation coefficients between estimates of food group intake assessed by repeated questionnaires ranged from 0.45 to 0.92. For men, Spearman correlation 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 vegetables 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, on the group level most median food group estimates based on photographic portion sizes were closer to the median intakes as assessed by 24-hour recalls than those based on standard portion sizes.
Conclusions: The questionnaire seems adequate for ranking Dutch EPIC subjects according to intake of most food groups, although the relative validity for some food groups, such as vegetables and fish, remains of concern.