  We derive a simple relational expression between the spin polarization ratio
of resistivity, $P_\rho$, and the anisotropic magnetoresistance ratio $\Delta
\rho/\rho$, and that between the spin polarization ratio of the density of
states at the Fermi energy, $P_{\rm DOS}$, and $\Delta \rho/\rho$ for nearly
half-metallic ferromagnets. We find that $P_\rho$ and $P_{\rm DOS}$ increase
with increasing $|\Delta \rho/\rho|$ from 0 to a maximum value. In addition, we
roughly estimate $P_\rho$ and $P_{\rm DOS}$ for a Co$_2$FeGa$_{0.5}$Ge$_{0.5}$
Heusler alloy by substituting its experimentally observed $\Delta \rho/\rho$
into the respective expressions.
