\begin{table}%T3
%\setlength{\tabcolsep}{0.5pt}
\caption{\label{tab3}Comparisons of our calculated WD~formation rate with previous results.}
\small%\centering
\par
\begin{tabular}{ccc}
\hline\hline\noalign{\smallskip}
Formation rate (pc$^{-3}$ yr$^{-1}$)     &   Sample  &   Reference   \\
\hline
\noalign{\smallskip} 
$2.58\times 10^{-13}$ & 531 DA~WDs from SDSS~& this work\\
$(0.1{-}2)\times 10^{-10}$ &   89 WDs  &   Green (\cite{Green1980})    \\
$(3.9{-}6.1)\times 10^{-13}$   &   353 DA~WDs from PG  &   Fleming et~al. (\cite{Fleming1986})    \\
$2.3\times10^{-12}$ &   &   Weidemann (\cite{Weidemann1991})    \\
$(7{-}10)\times 10^{-13}$  &   90 hot WDs from EUVE    &   Vennes et~al. (\cite{Vennes1997})    \\
$6\times10^{-13}$   &   348 DA~WDs from PG  &   Liebert et~al. (\cite{Liebert2005})   \\
\hline
\end{tabular}
\end{table}