Ascertainment models for human families selected through several affected children

Sampling models for families having normal and affected children and being selected through information about two or more of the affected ones have been developed. Such a model, a so-called ascertainment model, yields the conditional probability that a family has r affected children given that it has s children altogether and that it has been selected or ascertained with a probability which is proportional to a given power of the number of different groups of m less than or equal to r affected children. When the power equals zero or one the model is simplified considerably. If also m = 1 we get the well-known complete ascertainment and single ascertainment model as special cases.