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The authors assessed the reproducibility and validity of an expanded 131-item semiquantitative food frequency questionnaire used in a prospective study among 51, 529 men. The form was administered by mail twice to a sample of 127 participants at a one-year interval. During this interval, men completed two one-week diet records spaced approximately 6 months apart. Mean values for intake of most nutrients assessed by the two methods were similar. Intraclass correlation coefficients for nutrient intakes assessed by questionnaires one year apart ranged from 0.47 for vitamin E without supplements to 0.80 for vitamin C with supplements. Correlation coefficients between the energy-adjusted nutrient intakes measured by diet records and the second questionnaire (which asked about diet during the year encompassing the diet records) ranged from 0.28 for iron without supplements to 0.86 for vitamin C with …