Distribution of $S_{21}^{3/2}dn/dlog{S}_{21}$ as a function of the flux density, S₂₁, where dn is the surface number density of galaxies in a given log S₂₁ bin. This relation is used to determine the completeness of H I targets for all three surveys in different W₅₀ bins, following the practice of Haynes et al. (2011). For fair comparisons, the measurements in both ALFALFA and FASHI are limited to the redshift range of 0 < z < 0.05. However, HIPASS only has samples in 0 < z < 0.042. The orange, blue, green, and red circles are shown for the HIPASS, ALFALFA, FASHI south, and FASHI north galaxies, respectively. The solid lines in each panel are the best-fit error function. The vertical red dotted lines indicate the 50% completeness limit of FASHI north in each W₅₀ bin.