An easy method of calculating approximate recurrence risks using a multifactorial model of disease transmission.

In the usual form of the multifactorial model of disease transmission, calculation of recurrence risks is made difficult by the necessity to evaluate integrals involving the Normal distribution. It is suggested here that this becomes much easier if the Normal distribution is replaced by the Pareto distribution. Tables are given systematically comparing values of recurrence risk calculated on the Normal and Pareto models when information about two or three first degree relatives is available. Also, a more complicated pedigree is examined. It is shown from these comparisons that the Pareto model gives very similar results to the Normal model.