Estimating the contribution of individual risk factors to disease in a person with more than one risk factor.

Various measures have been proposed to express the excess risk of an outcome attributable to one particular risk factor, such as attributable risk and risk fraction. However, there is sometimes a need, both in epidemiological studies and in awarding compensation in legal cases, to simultaneously consider the contribution of several risk factors to a disease outcome, when a biological model is not available. We propose a method that allocates the proportional contribution of several risk factors to a disease outcome, based on the weighted contribution of the risk fraction for each risk factor. We demonstrate the use of this method using figures for renal cell carcinoma, and discuss the caveats in using this method for epidemiologic studies, and in awarding compensation in legal cases.