Precision and bias of food frequency-based measures of fruit and vegetable intakes

Accurate assessment of fruit and vegetable intakes is critical for cancer control research and public health surveillance. This report examines the bias and precision of two commonly used food frequency questionnaire methods to assess fruit and vegetable intakes: (a) the 5 A Day method, based on seven items; and (b) the summation method, based on adding total servings of all fruit and vegetable items on a comprehensive (100+ item) food frequency questionnaire. Data are from three studies in which 24-h dietary recalls, food records, or serum carotenoid concentrations could be used as criterion measures (n = 260, 1031, and 342). Studies differed markedly in distributions of participants' age, race/ethnicity, sex, and socioeconomic status. Mean intakes of total fruit and vegetables based on the 5 A Day method were consistently lower than those from either the summation method (3.11 versus 4.06), 24-h recalls (3.32 versus 4.07), or food records (3.11 versus 3.46; all P < 0.01), and this was due primarily to underestimates of vegetable intake. Correlations of the 5 A Day and summation measures with all criterion measures were similar and were consistently higher for fruit (range, 0.33-0.57) than for vegetables (range, 0.24-0.32). These results, which were consistent across diverse participant samples, suggest that the 5 A Day method yields both biased and imprecise measures of vegetable intake and that research to improve this measure is needed.