POPULATION ATTRIBUTABLE FRACTION AS A MEASURE OF HERITABILITY IN DICHOTOMOUS TWIN DATA.

In many genetic analyses of dichotomous twin data odds ratios have been used to test hypotheses on heritability and shared common environment effects of a given disease (Lichtenstein et. al., 2000, Ahlbom et. al., 1997, Ramakrishnan, et. al., 1992, 1996). However, estimates of these two effects have not been dealt with in the literature. In epidemiology, the attributable fraction (AF), a function of the odds ratio and the prevalence of the risk factor has been used to describe the contribution of a risk factor to a disease in a given population (Leviton, 1973). In this article, we adapt the AF to quantify the heritability and the shared common environment. Twin data on cancer, gallstone disease and phobia are used to illustrate the applicability of the AF estimate as a measure of heritability.