\begin{table}%t4
\caption{\label{tab:summary}The source breakdown according to the absorption properties. See Sect. 4.3 for details.}
%\centerline
{
\begin{tabular}{lcc}
\hline\hline 
\multicolumn{1}{l} {Source}&
\multicolumn{1}{c} {X-ray}&
\multicolumn{1}{c} {Control} \\
Type& Sample &  Sample \\ 
& (1) & (2)  \\
 \hline  
\nh~$<~10^{22}$     &  13--52{\%}  & 85{\%} \\
\nh~$\geq~10^{22}$  & 48--87{\%}  & 15{\%} \\
QSO2s             & 43--60{\%}   &  5{\%} \\
N. of Sources      &  23       &  20 \\
\hline                                    
\end{tabular}}            
Column: 
(1) Percentage of objects for each source type found in our sample (i.e. for the absorbed sources we report the maximum  and minimum value derived assuming the best fit value and the lowest value at 90{\%} confidence level for the \nh~parameter, respectively);
(2) percentage of objects for each source type in the control sample (20 objects).
\end{table}