\begin{table}%t1
\par
    \caption{\label{tab:surveys}Summary of surveys.}
  \small%\centerline
{
  \begin{tabular}{lcccc}
    \hline
    \hline
            &  & \multicolumn{2}{l}{Soft (0.5$-$2~keV)}   \\
        Survey &  Flux limit (\cgs{}) & Area (deg$^{2}$) & $N_{\rm total}$$^a$ & $N_{\rm AGN}$$^b$ \\
        \hline\noalign{\smallskip}
    RBS    & $2.5 \times10^{-12}$  & 20~300 & 953 (100\%) & 310    \\
    RIXOS8 & $8.4 \times10^{-14}$  & 4.44 & 105 (100\%) &  40    \\
    RIXOS3 & $3.0 \times10^{-14}$  & 15.77 & 296 (94\%) & 182    \\
    XMS~   & $1.5 \times10^{-14}$  & 3.33 & 210 (96\%) &  178    \\
    UDS    & $1.2 \times10^{-15}$  & 0.36 & 94 (95\%)$^c$ &  73$^c$    \\
    CDF-S  & $5.5 \times10^{-17}$  & 0.12 & 307 (99\%)$^c$ & 226$^c$    \\
       \hline
            &  & \multicolumn{2}{l}{Hard (2$-$10~keV)}  \\
    %\noalign{\smallskip}
    %\hline
    %\noalign{\smallskip}
    Survey &  Flux limit (\cgs{}) & Area (deg$^{2}$) & $N_{\rm total}$$^a$ & $N_{\rm AGN}$$^b$ \\
    %\noalign{\smallskip}
    \hline
    \noalign{\smallskip}
    AMSS   & $3.0 \times10^{-13}$  & 68 & 87 (99\%) &  79	 \\
    XMS~   & $3.3 \times10^{-14}$  & 3.33 & 159 (84\%) & 120    \\
    CDF-S  & $4.5 \times10^{-16}$  & 0.11 & 251 (99\%)$^c$ & 236$^c$    \\
%    \noalign{\smallskip}
   % \hline
    \hline
 %   \noalign{\smallskip}
        &  &  \multicolumn{2}{l}{Ultrahard (4.5$-$7.5~keV)}  \\
    %\noalign{\smallskip}
    %\hline
    %\noalign{\smallskip}
    Survey &  Flux limit (\cgs{}) & Area (deg$^{2}$) & $N_{\rm total}$$^a$ & $N_{\rm AGN}$$^b$ \\
    \noalign{\smallskip}
    \hline
    \noalign{\smallskip}
    HBSS   & $7.0 \times10^{-14}$  & 25.17 & 67 (97\%) &  62    \\
    XMS~   & $6.8 \times10^{-15}$  & 3.33 & 70 (86\%) &  57    \\
%    \noalign{\smallskip}
     \hline
  %  \noalign{\smallskip}
   \end{tabular}}
   \smallskip
    $^a$ Total number of X-ray sources in the sample (identification completeness in parenthesis). \\
     $^b$ Number of identified AGN in the sample. \\
     $^c$ Including photometric redshifts (see text). \\ 
\end{table}