  The inference of the Milky Way halo mass requires modelling the phase space
structure of dynamical tracers, with different tracers following different
models and having different levels of sensitivity to the halo mass. For
steady-state models, phase correlations among tracer particles lead to an
irreducible stochastic bias. This bias is small for satellite galaxies and dark
matter particles, but as large as a factor of 2 for halo stars. This is
consistent with the picture that satellite galaxies closely trace the
underlying phase space distribution of dark matter particles, while halo stars
are less phase-mixed. As a result, the use of only $\sim 100$ satellite
galaxies can achieve a significantly higher accuracy than that achievable with
a much larger sample of halo stars.
