An investigation of recall bias in the reporting of past food intake among breast cancer cases and controls.

A nested case-control study was conducted within the Canadian National Breast Screening Study to examine whether there was evidence for biased reporting of past food intake. A total of 325 case patients with breast cancer and 628 matched control subjects completed a self-administered food frequency questionnaire in 1988, recalling their diets originally reported on enrollment into the National Breast Screening Study between 1982 and 1985. Recall of food items was very similar for case patients and control subjects. The magnitude of the odds ratios for the association between these food groups and breast cancer from the prospectively and retrospectively collected data was not systematically different. There was little evidence for recall bias in the reporting of past food intake from these data.