\begin{table}%t1
  \caption{Mean redshift and luminosity ($\pm 1\sigma$) of the mid-IR samples.\label{tab1}}
  %\centerline
{  \begin{tabular}{ccccc}
    \hline\hline 
     Sample & \multicolumn{2}{c}{IRAS } & \multicolumn{2}{c}{ISO  } \\
     & $\langle z\rangle$ & $\langle {\rm log}~ L_{15}\rangle ^{a}$ & $\langle z\rangle$ & $\langle {\rm log}~ L_{15}\rangle$ \\
    \hline
    Type-1 & $0.03\pm0.02$ & $43.87\pm0.87$ & $1.23\pm0.71$ & $45.22\pm0.78$ \\
    Type-2 & $0.02\pm0.01$ & $43.66\pm0.68$ & $0.28\pm0.20$ & $43.90\pm0.69$ \\
    \hline
  \end{tabular}}
\par
  \smallskip
        $^{a}$ {12~$\mu$m luminosities from rms have been 
        converted to 15~$\mu$m using the adopted SED. In particular the $Circinus$ 
        SED was adopted for type-2 AGN (see Sect.~3.1).}
\end{table}