\begin{table}%T4
\caption{\label{t4}Differences in dex on plasma parameters and
 chemical abundances adopting data from this work
 versus data taken from the literature. The number of
 analyzed PNe in common is given in parenthesis.}
%\centerline
 {
\begin{tabular}{lcccccc}
\hline\hline
    Sample$^{a}$ &
    $\Delta$ log~\Te(N~{\sc ii}) &
    $\Delta$ log~\Te(O~{\sc iii}) &
    $\Delta$ log~\Ne(S~{\sc ii}) &
    $\Delta$ log~O/H &
    $\Delta$ log~N/O &
    $\Delta$ log~S/Ar \\
\hline
    {\it G}   & 0.01 ~~(~8) & 0.02 ~~(~8) & 0.13 ~~(~9) & 0.04 ~~(~9) & 0.32 ~~(~9) & 0.20 ~~(~5) \\
    {\it ECM}  & 0.02 ~~(~9) & 0.02 ~~(~9) & 0.29 ~~(10) & 0.10 ~~(12) & 0.17 ~~(12) & 0.11 ~~(~7) \\
    {\it WL}   & 0.02 ~~(~8) & 0.01 ~~(~8) & 0.06 ~~(~8) & 0.04 ~~(~8) & 0.18 ~~(~8) & 0.07 ~~(~4) \\
    {\it EBW}  & 0.08 ~~(10) & 0.04 ~~(10) & 0.13 ~~(22) & 0.19 ~~(20) & 0.27 ~~(20) & 0.15 ~~(10) \\
\hline 
\end{tabular}}
\medskip
\par
$^a$ Sample {\it G} includes objects in common with
           original PNe observations of G\'orny et~al. (\cite{Gorny04});
           sample {\it ECM} -- Escudero \& Costa (\cite{Escudero01}) or Escudero et~al. (\cite{Escudero04});
           sample {\it WL} -- Wang \& Liu (\cite{Wang07})
           and {\it EBW} -- Exter et~al. (\cite{Exter04}).
\end{table}