At each chromosome position for each sibling pair, the variance in IBD 0, IBD 1, and IBD 2 estimates is divided by the variance in the absence of marker information (for siblings, this is 0.5). The mean of this measure is subtracted from 1. If the posterior IBD status is known with certainty for all pairs, the variance is 0 and the information is 1. This measure was then computed on all relative pairs except for parent-offspring, where the prior variance is 0 (since Pr(IBD = 1) = 1.0), notwithstanding a new mutation. The results for the sibling pairs are presented in Figure 3.
