Mean rank correlation, based on 1,000 replications, between squared difference of trait values of a sib pair and estimated i.b.d. scores at 100 ordered markers, with the use of simulation parameter values α=3, σ2=1, p=.7, ρ=.6, and (a) β=0, (b) β=1, and (c) β=2, on the basis of data from 100 sib pairs.