This Letter presents results of new high-resolution {OMEGA} = 1 cold + hot dark matter (CHDM) and cold dark matter (CDM) simulations. Properties of groups in these simulations reflect the lower small-scale velocities and the greater tendency to form distinct filaments on both small and large scales in CHDM as compared to CDM. The fraction of galaxies in groups and the median group rms velocity are found to be powerful discriminators between models. We combine these two features into a very robust statistic, median group rms velocity v_gr_(f_gr_) as a function of the fraction f_gr_ of galaxies in groups. Using this statistic, we compare "observed" simulations to CfA data in redshift space in a careful and consistent way. We find that CHDM remains a promising model, with for example v_gr_(0.45)~ 125 +/- 25 km s^-1^ in agreement with the CfA data, while CDM with bias b = 1.0 (COBE-compatible) or b = 1.5, both giving v_gr_(0.45)~400 +/- 25 km s^-1^, can be virtually ruled out. Using median M/L, the observed value of {OMEGA} is 0.10 (CHDM) to 0.38 (CDM).
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Nolthenius et al. (1994) studied this question.