\begin{table}%t1
\caption{ General characteristics of the data analyzed in this work. 
The number of detections and censored data are reported for the interesting
parameters for the whole sample of objects (Cols.~2 and 3), for the 
Seyfert~1 galaxies (Cols.~4 and 5), and for the Seyfert~2 objects (Cols.~6 
and 7). The 90\% confidence interval limits were used for censored data and
the detected values were defined if determined with a 99\% confidence level (Dadina \cite{Dadina2007})}\label{tab1}
%\centering
\par
\begin{tabular}{ l  c c  c c  c c }
\hline
\hline
\multicolumn{1}{c}{Parameter}&\multicolumn{2}{ c }{Tot. Sample}&\multicolumn{2}{ c }{Seyfert~1}&\multicolumn{2}{c}{Seyfert~2}\\
& Det.&  Cens. &  Det. & Cens. & Det. & Cens.\\
\hline
$N_{\rm H}$ & 83 & 80 & 31 & 53 & 52 & 27 \\
$EW$& 129 & 7 & 66 & 4 & 63 & 3 \\
$R$& 68 & 18 & 46 & 9 & 22 &9 \\
$E_{\rm c}$ & 33& 51& 27& 26& 6 & 25\\
 \hline 
\end{tabular}
\end{table}