Validity and reproducibility of a food frequency questionnaire designed for residents in north China.

The objective of this study was to evaluate the validity of a Xi'an food frequency questionnaire (FFQ) designed for application in an international case-control colorectal cancer study. The FFQ was administered to 125 participants twice over 1-year interval. Four 24-hour dietary recalls (24-HDRs) were conducted with the same participants in each season of the year. Comparative validation was assessed by comparing the nutrient intakes derived from the 24-HDRs and the FFQ-2, and reproducibility was estimated by comparing the nutrient intakes from two FFQs. In the validation study, the mean deattenuated correlation coefficients for nutrients between the 24-HDRs and the FFQ-2 ranged from 0.35 to 0.84 in the males. The female results were slightly lower than the male's. The mean percentage of classification into the same quartile was 38% for the males and 35% for the females. In the reproducibility study, the mean crude correlation coefficients between the two FFQs were from 0.41 to 0.68 in the males and from 0.36 to 0.66 in the females. The newly developed Xi'an FFQ appears to be reasonably valid and reliable for most nutrients but would benefit from the addition of nutritional supplements and seasonings for assessing dietary intake in older persons in Xi'an, China.