The use of polytomous dual response data to increase power in case-control studies: an application to the association between dietary fat and breast cancer.

Computer simulation has been used to compare various methods for analyzing data from case-control studies when two response variables are available to measure a risk factor. When such variables are continuous or polytomous, and a dose-response relationship exists, it is concluded that power may be increased by including individuals who are discordant on their responses. Failure to use the most appropriate method can lead to a substantial loss in power. The results are illustrated by reanalysis of data from an earlier case-control study of diet and breast cancer. This reanalysis has strengthened the evidence for a positive association between saturated fat intake and risk of breast cancer, with some suggestion that this association is limited to premenopausal women, in whom the increase in risk may be substantial.