case, if the ancestral match is suitable. Moreover, to be useful in the association analysis, every unrelated case must be matched to an unrelated control. Thus we first match unrelated cases to one or more unrelated controls. These individuals are then set aside as matched strata. Next we use fullmatch to cluster trio probands with the remaining unrelated controls. If fullmatch defines a cluster that includes multiple trio probands, one proband is selected at random to remain in the stratum. The extra probands are each moved to their own strata together with their ancestrally identical pseudo-controls. We now have K strata consisting of 1 case and nk controls in stratum k.
