Fluctuations in odds ratios due to variance differences in case-control studies.

Abstract

If small effects of exposure on disease outcome are to be appropriately assessed, it is necessary to consider all potential sources of the fluctuation of relative odds. The authors consider the impact of differential variance in case and control exposure reports on the magnitude of the observed relative odds. With equal dispersion of case and control exposure, a difference in mean exposure generally produces a dose-response increase in relative odds. The combination of equal mean and unequal dispersion of case and control exposure produces a curvilinear pattern of relative odds. Greater mean exposure and dispersion of exposure among cases produce odds ratios lower than those that would be observed if dispersion among cases and controls were equal. Conversely, less dispersion among cases than among controls produces higher relative odds estimates. Differential error as a source of differential dispersion constitutes a potentially important source of bias.