A resolution of the ascertainment sampling problem. I. Theory.

We consider the "ascertainment problem" arising when families are sampled by a nonrandom sampling process and, for the purpose of estimating genetic parameters, some assumption must be made about the process by which families enter the sample. A resolution of this problem, involving conditioning the likelihood of the sample on that part of the data relevant to ascertainment, is put forward. Numerical examples illustrating the properties of the procedure are provided.