give results below not only for our “best” samples but also for samples where the various constraints are relaxed. Thus, we consider samples in which 1) both morphology and isolation requirements are applied (our preferred case), 2) the isolation requirement is removed, 3) the morphology requirement is removed, and 4) both morphology and isolation requirements are removed. For each case, we compare results for the two allowed ranges of $V_{max}$ and we also examine the effect of loosening the radial velocity constraint to $V_{ra} < 0$.

Fig. \[hist\] gives histograms of the distribution of $A_{200}$ for a sample in the narrow $V_{max}$-range with our preferred isolation, morphology and radial velocity cuts, as well as for three samples with the same $V_{max}$ and $V_{ra}$ cuts but with reduced morphology and isolation requirements. Fig. \[narrow\_ratio\_cumu\_dist\] presents these same distributions in cumulative form and compares them with the corresponding distributions for samples with the loosened circular velocity requirement, $150{{\rm \,km\,s^{-1}}}\le V_{max} < 300{{\rm \,km\,s^{-1}}}$. In both plots black curves refer to class (1) samples for which both isolation and morphology cuts are imposed, while red, green and blue curves refer to samples in classes (2), (3) and (4) respectively. Results for the broader 