  The Korringa ratio, $\cal K$, obtained by taking an appropriate combination
of the Knight shift and nuclear spin-lattice relaxation time, is calculated at
finite temperature, $T$, in the three-dimensional electron gas model, including
the electron-electron interaction, $U$, and non-magnetic impurity scatterings.
$\cal K$ varies in a simple way with respect to $U$ and $T$; it decreases as
$U$ is increased but increases as $T$ is raised. However, $\cal K$ varies in a
slightly more complicated way with respect to the impurity scatterings; as the
scattering rate is increased, $\cal K$ increases for small $U$ and low $T$, but
decreases for large $U$ or high $T$ regime. This calls for a more careful
analysis when one attempts to estimate the Stoner factor from $\cal K$.
