\begin{table}%t4
%\centering
\par
\caption{\label{samples} Statistical properties of the $\sigma$-drop and
control samples, showing mean and median values of the four parameters
used for matching the samples.}
\begin{tabular}{l   c c   c c}
\hline\hline
 &\multicolumn{2}{c}{$\sigma$-drop sample} &\multicolumn{2}{c}{Control sample}
\\
Property & mean & median & mean & median \\
\hline
Distance (Mpc)         &  18.24 &  17.25 &  19.47 &  18.15\\
$B$ Magnitude       & $-$20.53 & $-$20.70 & $-$20.48 & $-$20.32\\
$d/D$                    &   0.66 &   0.71 &   0.63 &   0.64\\
Type &   2.2 &   2.5 &   2.3 &   2.5\\
\hline
\end{tabular}
\end{table}