Probability distribution function of the 3D true intervelocities between members of galaxy pairs in the IGP Catalog (deprojected from radial velocity differences) for the subsample of 7449 fairly isolated pairs ρ >  5 (see text). Upper panel: deprojection method used here is the two-bin difference, with bins of 26, 28 and 30 km s⁻¹. Lower panel: two-bin difference deprojection method, for a bin width 30 km s⁻¹, accompanied by the estimated uncertainties derived from numerical simulations (±1 σ, gray curves). The uncertainties derived from the simulation clearly agree with the fluctuations observed for different bins in the left panel. No matter which bin width and method are used, a probability peak at ≈150 km s⁻¹ appears to be stable.