Relative validity of a short qualitative food frequency questionnaire for use in food consumption surveys

Background: The aim of the present study was to assess the relative validity of a self-administered qualitative food frequency questionnaire (FFQ) applied in the Belgian food consumption survey. Methods: Comparison of food consumption data from an FFQ with 7-day estimated diet records (EDR) was made in a sample of 100 participants (aged 15-90 years). The FFQ comprised a total of 50 foods. Both FFQ and EDR foods were categorized into 15 conventional food groups. Results: De-attenuated Spearman rank correlation coefficients between the FFQ and the EDR ranged from -0.16 for potatoes and grains to 0.83 for alcoholic beverages, with a median of 0.40 for all 15 food groups. The proportion of participants classified in the same tertile of intake by the FFQ and EDR ranged from 32% for potatoes and grains to 76% for alcoholic beverages. Extreme classification into opposite tertiles was < 10% for milk and soy products, alcoholic beverages, fried restgroup foods and fats. Conclusion: Notwithstanding the short nature and the absence of portion size questions, the FFQ appears to be reasonably valid in both genders and across different age categories for most food groups. However, for the food groups bread and cereals, potatoes and grains, and sauces, estimates should be interpreted with caution because of poor ranking agreement.