Reproducibility of a food frequency questionnaire for use in ocular research. Eye Disease Case-Control Study Group

Assessment of nutritional factors was an ancillary component of the Eye Disease Case-Control Study sponsored by the National Eye Institute. This multicenter study was designed to evaluate the role of potential risk factors for a number of retinal disorders. The authors examined the reproducibility of the food frequency questionnaire used in this study.

A semiquantitative food frequency questionnaire, designed for use in this study, was self-administered by participants. To evaluate the reproducibility of this dietary questionnaire, a subsample of 325 participants completed a second questionnaire within 12 to 18 months of the first. Pearson product-moment coefficient was used to assess the correlation between the log of calorie-adjusted nutrient scores, and Spearman correlations were used for specific food items.

The responses for intake of 60 food items in the questionnaire were reasonably consistent. Correlation coefficients for individual food items ranged from 0.40 to 0.82. Pearson correlation coefficients for logs of calorie-adjusted intake of nutrients ranged from 0.38 to 0.75. Nutrients of interest in eye disease include total protein (r = 0.57), total fat (r = 0.71), saturated fats (r = 0.69), carotene (r = 0.61), vitamin C (with supplements, r = 0.66), vitamin E (with supplements, r = 0.69), and zinc (with supplements, r = 0.43). Partial correlations controlling for age, sex, and clinical center were similar.

These findings indicate that the food frequency questionnaire used in this study provides reasonably reproducible dietary information.