We describe a simple general objective method for determining the distribution functions (counts in cells) of biased subsamples. This method does not depend on any specific definition of a "cluster." Applying this to morphological subsets of the UGC and ESO catalogs, and to the IRAS catalog, quantifies the excess clustering of early-type E + S0 galaxies relative to Sa + Sb spirals. Spirals are distributed nearly randomly, while the average probability of finding an elliptical in a region containing M galaxies is ρ(M) ~ M^0.3^. If the present galaxy distribution is similar to the distribution when stripping and merging occurred, then these processes do not account for the observed morphology-density relation of ellipticals and spirals. Models in which stripping or merging occurred at high redshifts are constrained by the requirement that they evolve into the presently observed distribution functions of ellipticals and spirals, which are consistent with simple gravitational clustering. These morphology-density relations may be consistent with gravitational segregation if the average masses associated with ellipticals are several times greater than those of spirals. It may also reflect the initial density threshold for different galaxy types.
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Lahav et al. (1992) studied this question.