  There have been the approximate analytic solution \cite{Silveria} and several
approximate analytic forms \cite{0508156,Carroll,0303112} of the growth factor
$D_{g}$ for the general dark energy models with the constant values of its
equation of state $\omde$ after Heath found the exact integral form of the
solution of $D_{g}$ for the Universe including the cosmological constant or the
curvature term. Recently, we obtained the exact analytic solutions of the
growth factor for both $\omde = -1$ or $-\fr{1}{3}$ \cite{SK1} and the general
dark energy models with the constant equation of state $\omde$ \cite{SK3}
independently. We compare the exact analytic solution of $D_{g}$ with the other
well known approximate solutions. We also prove that the analytic solutions for
$\omde = -1$ or $-\fr{1}{3}$ in Ref. \cite{SK1} are the specific solutions of
the exact solutions of the growth factor for general $\omde$ models in Ref.
\cite{SK3} even though they look quite different. We scrutinize the issue of
using the well known parameterizations of the growth index and its parameter
given in Ref. \cite{WS} to obtain the growth factor for general dark energy
models. We also investigate the possible extensions of the exact solution of
$D_{g}$ to the time-varying $\omde$ for the comparison with observations.
