An assessment, and reproducibility of food frequency data provided by hospital controls

In order to assess the comparability and reproducibility of information from a questionnaire used in a case-control study on digestive tract cancers conducted in Italy, a total of 400 subjects were randomly selected from a large sample of hospital controls and contacted at home to repeat the interview. Of these, 294 (73%) subjects were re-interviewed. Mean values of intake were computed for the 400 subjects selected, and among the 294 responders for the first and second interview. These values were comparable, most of them being within a 10% range. Spearman correlation coefficient (r(s)) values of consumption between the first and second interview were > 0.65 for consumption of pastries, pasta or rice, bread, fish, milk, green vegetables, eggs and apples; between 0.50 and 0.65 for meat, chicken, liver, ham, cold cuts, cheese, fruit, cabbage, carrots, tomatoes, peppers, salad, citrus fruit and melon; and lower than 0.50 for a few infrequently eaten foods. For all foods, the estimated average weekly intake in the second interview increased consistently and substantially with increasing tertile of the first interview. This study shows a satisfactory comparability of dietary information from subjects interviewed at home with that provided during their original interview in the hospital, and a good reproducibility of information collected in the two settings.