  Measurements of the cosmological density parameter (Omega) using techniques
that exploit the gravity-induced motions of galaxies yield, in linear
perturbation theory, the degenerate parameter combination beta=Omega^{0.6}/b,
where the linear bias parameter b is the ratio of the fluctuation amplitudes of
the galaxy and mass distributions. However, the relation between the mass and
the galaxy density fields depends on the complex physics of galaxy formation,
and it can in general be non-linear, non-local, and stochastic. There is a
growing consensus that the one-parameter model for bias is oversimplified. This
leaves us with the following question: What is the quantity that is actually
being measured by the different techniques? In order to address this question,
we present estimates of beta from galaxy distributions constructed by applying
a variety of biased galaxy formation models to cosmological N-body simulations.
We compare the values of beta estimated using two different techniques: the
anisotropy of the redshift-space power spectrum and an idealized version of the
POTENT method. In most cases, we find that the bias factor b=Omega^{0.6}/beta
derived from redshift-space anisotropy or POTENT is similar to the large-scale
value of b_{sigma}(R) defined by the ratio of rms fluctuation amplitudes of the
galaxy and mass distributions. However, non-linearity of bias and residual
effects of non-linear gravitational evolution both influence beta estimates at
the 10-20% level.
