where and are the vectors of the probabilities
that IBD = 1 and 2, respectively, for all the relative pairs in
pedigree i. The score statistic, denoted by S, is defined as S
= b2/Var(b) if b > 0; S = 0 otherwise, where b = Σi (πi -
E(πi))t(vi - E(vi)) and, for sibship data, Var(b) =
Var(π)ΣiΣk