Development and relative validity of a food frequency questionnaire for the estimation of intake of retinol and β‐carotene

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Abstract
The aim of this study was to develop and validate a semiquantitative food frequency questionnaire to classify individuals according to their intakes of retinol and β‐carotene. Food items for the questionnaire were selected both on the basis of their contribution to total population intake of retinol and β‐carotene and on the proportion of between‐person variation explained, which was as calculated from data of two study populations in the Netherlands. Thus, 15 products containing retinol and 15 products containing β‐carotene were selected. These contributed over 90% to the total intake and explained 99% of the variation of retinol and β‐carotene, respectively. The questionnaire was validated against a dietary history in a population of 82 women (aged 30–49 years). The time elapsed between the two interviews was (on average) 25 days. Spearman rank‐order correlation coefficients comparing the questionnaire with the dietary history were 054, 0.59, and 0.64 for retinol, β‐carotene, and total vitamin A, respectively. The proportion of exact agreement in the two extreme categories of vitamin A intake, based on quintiles, was 56%. The corresponding gross misclassification (from 1 extreme category into the opposite) was 3%. These data indicate that a very short questionnaire can classify subjects into categories according to their vitamin A intake.