REPRODUCIBILITY AND VALIDITY OF A FOOD FREQUENCY QUESTIONNAIRE IN A CASE-CONTROL STUDY ON BREAST-CANCER

A 110-item food frequency questionnaire was tested among 152 community controls of the Kuopio Breast Cancer Study. They completed the questi onnaire twice and kept two 7-day diet records at 3-month intervals. Th e intraclass correlations for nutrients varied from 0.49 (thiamine wit h supplements) to 0.81 (lactose), and for foods from 0.52 (poultry) to 0.84 (alcoholic drinks). The Pearson correlations between the first f ood frequency questionnaire and the 14-day diet records, after adjustm ent for energy, varied for nutrients from 0.18 (thiamine without suppl ements) to 0.80 (alcohol), and for foods from 0.30 (inner organs) to 0 .90 (coffee). Comparison of quintile classification between the two me thods is reasonably accurate when observed restrictions concerning som e nutrients and foods are taken into account. A Low association (r = 0 .12) was observed between toenail selenium and dietary selenium intake , indicating the difficulty of estimating selenium intake in the Finni sh diet.