  The ability of semi-classical transport models to correctly simulate Pauli
blocking and Bose enhancement is discussed. In the context of simple quantum
mechanical systems, it is shown that using $(1 \pm f)$ enhancements is
inadequate to describe systems far from equilibrium. The relaxation of $(1 +
f)$ descriptions toward equilibrium is studied both in the context of simple
models, including a hot pion gas confined to a box. We give simple estimates
for the characteristic number of collisions for a system to relax toward
equilibrium.
