Differential misclassification bias and dietary recall for the distant past using a food frequency questionnaire

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Abstract
Cases (n = 263) and controls (n = 200) returned self‐administered food frequency questionnaires in 1980–1982 and again in 1986 as part of a case‐control study of breast cancer. The questionnaires asked about consumption of specific food items as recalled for four different age periods. K‐statistics comparing responses in the first and second questionnaires were generally similar for cases and controls and were consistent across the different age periods. The influence of recent dietary change on dietary recall diminished for the more distant past. The food frequency questionnaire was found to be more reliable for specific food items for the distant past than for the more recent past. Differential misclassification bias between cases and controls was less apparent for the more distant past. The frequency and interpretation of missing values is discussed.