\begin{table}%t3
\caption{Comparison of the velocity dispersions derived in this study and in
previous works. The table columns are: Offset: mean offset between this study
and the one in Col.\ 1; rms: dispersion among the mean value; Exp.\ rms:
dispersion expected from the errors; $z$: result of a \mbox{$z$-test} to contrast the
hypothesis of a null offset (a value higher than 1.96 allows us to reject
the hypothesis with a significance level lower than 0.05); $N$: number of
galaxies in each comparison. Units are km~s$^{-1}$.\label{tab-comparasigma}}
%\centering
\par
\small
\begin{tabular}{lccccc} 
\hline\hline
Study &   Offset     & rms & Exp.\ rms & $z$ & $N$\\
\hline
G93   &   12.5       &19.5 & $\;\;$9.6   & 3.1& 33\\
T98   &   13.7       &15.1 & 10.7   & 4.8& 52\\      
M02   &   17.4       &21.2 & 11.0   & 1.7& 12\\
K01   &   12.9       &15.8 & 11.9   & 3.5& 31 \\
\hline
\end{tabular}
\end{table}