A note on the power provided by sibships of sizes 2, 3, and 4 in genetic covariance modeling of a codominant QTL

The contribution of size 3 and size 4 sibships to power in covariance struc ture modeling of a codominant QTL is investigated. Power calculations are b ased on the noncentral chi-square distribution. Sixteen sets of parameter v alues are considered. Results indicate that size 3 and size 4 sibships prov ided large increases in power over size 2 sibships. On average a size 3 (4) sibship is 3 (6 to 7) times as informative as a size 2 sibship. The increa se in power does not depend on the specific effects sizes of the independen t variables in the model. These findings extend results presented by Fulker and Cherny (1996) and Schork (1993). We consider the informativeness of th e size 2, 3, and 4 sibships, which differ in the unique configuration of IB D sharing. Three of the 10 size 3 and 7 of the 36 size 4 sibships are parti cularly informative. The results presented concern random (unselective) sam pling but do have implications for selective sampling.