Reproducibility and validity of a food-frequency questionnaire designed for use in girls age 7 to 12 years

This study focused on a food-frequency questionnaire (FFQ) designed to measure nutrient intake in girls aged 7 to 12 years, inclusive. The instrument's reproducibility and validity were assessed using food records (FRs) as "gold standards" of measurement. Log-transformed nutrient intake estimates were compared from two FFQs and between FFQs and FRs. Intraclass correlation coefficients measuring the reproducibility of the FFQ ranged from 0.11 (starch) to 0.69 (fiber). Intraclass correlation coefficients measuring agreement between FFQ and 14-day FR data varied between 0.15 (starch) and 0.68 (vitamin B₂) for the first, and between 0.06 (starch) and 0.95 (vitamin B₁) for the second FFQ. FFQs were in the best agreement with FRs for the following nutrients: fiber, vitamin B₁, vitamin B₂, vitamin C, and beta-carotene. Joint classifications revealed that overall, 36% of subjects were similarly categorized by FFQ and FR, and 70% of those in the lowest or highest FR quartiles were found in the lowest or highest two FFQ quartiles, respectively.