\begin{table}%t1
\caption{Constraints on cosmological parameters $\Omega_{\rm M}$ and $w_{\rm Q}$ found in the
literature under the assumption of perfectly flat universes. 
The last column quotes the data sets used in each work.}
\label{tabla}
%\centerline
{\begin{tabular}{llll}
\hline\hline
Author & $\Omega_{\rm M}$ & $w_{\rm Q}$ & Data\\
\hline
\citet{roukema02}    & $0.25 \pm 0.10$   & $[-1.0,-0.5]$ & 10K 2dFQSO$^1$ \\
\citet{tegmark04}    & $0.329 \pm 0.074$ & $-0.92\pm0.30$ & WMAP$^2$ + SDSS MGS$^3$\\
\citet{eisenstein05} & $0.326 \pm 0.037$ & $-0.80\pm0.18$ & WMAP + SDSS MGS + LRG$^4$ \\
\citet{wang06}       & ...             & $\rm -0.885^{+0.109~+0.206}_{-0.111~-0.227}$ & 
R04$^5$ WMAP3$^6$ + SNIa + LRG \\
\citet{wang06}       & ...             & $\rm -0.999^{+0.082~+0.159}_{-0.083~-0.168}$ &  A06$^7$ WMAP3 + SNIa + LRG \\
\citet{arielsan06}   & $0.241\pm0.024$ & $\rm -0.85^{+0.18}_{-0.17}$ & WMAP + 2dFGRS$^8$ \\
\citet{spergel07}    & $0.238\pm0.015$ & $-0.967\pm0.073$ & WMAP3 + SNLS$^9$ \\
This work            & $0.21\pm0.02$ & $-0.93\pm0.04$ & DR6 SDSS QSO \\
\hline
\end{tabular}}
\medskip
\par
1:~Quasars from the 10~K release of the 2 degree Field Quasar Redshift 
Survey, \citet{croom01}.\\
2:~First year Wilkinson Microwave Anisotropy Probe, \citet{spergel03}.\\
3:~Main Galaxy Sample, \citet{mgs}.\\
4:~Luminous Red Galaxies, \citet{eisenstein01}.\\
5:~\citet{riess04}.\\
6:~Third year Wilkinson Microwave Anisotropy Probe, \citet{spergel07}.\\
7:~\citet{astier06}.\\
8:~2 degree Field Galaxy Redshift Survey, \citet{2df}.\\
9:~Supernovae Legacy Survey, \citet{astier06}.
\end{table}