\begin{table}%T1
%\centering
\small
\caption{Number statistics of the four groups.} \label{t1}
\begin{tabular}{l@{\hspace{3.5mm}}c@{\hspace{3mm}}c@{\hspace{3mm}}c@{\hspace{3mm}}c}     % 7 columns
%
\hline\hline
%
Objects            & COAS      & COES   & Featureless & Others \\
%
\hline
%
Total              & 104       & 9        & 60          & 28        \\
IRE                & 34 (33\%) & 7 (78\%) & 32 (53\%)   & 10 (36\%) \\
%no IRE             & 70/67\% & 2/22\% & 28/47\%     & 18/64\% \\
X-ray            & 39 (38\%) & 4 (44\%) & 19 (32\%)   & 19 (68\%) \\
%no X-ray         & 65/62\% & 5/56\% & 41/68\%     & 9 /32\% \\
IRE and X-ray    & 19 (18\%) & 4 (44\%) & 10 (17\%)   & \ \ 6 (21\%) \\
IRE and/or X-ray & 54 (52\%) & 7 (78\%) & 41 (68\%)   & 23 (82\%) \\
%no X-ray, no IRE & 50/48\% & 2/22\% & 19/32\%     & 5 /18\% \\
\hline
\end{tabular}
\end{table}