Reproducibility of nutrient intake in a food frequency questionnaire used in a general population.

This study evaluates the reproducibility of nutrient intake in a 45-item food frequency questionnaire (FFQ). The FFQ was mailed in 1980 to persons eligible to participate in a large cohort study on diet and cancer risk; a follow-up version with 75 food items was mailed in 1988 to selected original participants. A random sample of 500 men and 500 women from the New York State general population was selected from individuals who responded to both waves of the study. The subjects' 1988 responses were compared with their original 1980 responses; Pearson's correlations ranged from 0.25 for retinol to 0.55 for vitamin C with or without supplements and vitamin E with supplements in women. Reproducibility of nutrient intake in this questionnaire indicates that brief FFQs may be a useful tool to study nutrient intake and chronic disease relationships, although they are subject to substantial measurement error and dietary change.