Affected sib-pair tests for linkage: Type I errors with dependent sib-pairs

We compared the robustness of affected-sib-pair (ASP) tests for multiple-affected sibships. Forming all possible pairs increases the type I errors only slightly whereas the most used weighting procedures decrease the efficiency of the tests. Another weighting procedure accounting for the reduction of variance of the weighted identical by descent (IBD) information appears robust. Missing parental marker data leads to a decrease of type I errors in all cases. © 1997 Wiley-Liss, Inc.