\begin{table}%t2
\caption{Groups of data considered for methods that constrain quantities related to $\frac{\Delta \alpha}{\alpha}$.}\label{data2}
%\centerline
 {\small  \begin{tabular}{ccccc}
\hline \hline
 Method & Redshift or redshift interval&   Quantity measured &$\frac{\Delta \alpha}{\alpha} \pm \sigma$ & Reference     \\ 
$(1)$ & $(2)$ & $(3)$& $(4)$ &$(5)$\\ \hline
 Optical and radio lines & $0.23 < z < 2.4$&   $\alpha ^2g_{\rm p}\frac{m_e}{m_p}$     &$0.32\pm0.50$& $(1)$  \\ 
 Molecular and radio lines & $z=0.69$&   $\alpha ^2g_{\rm p}$  &$-0.08 \pm 0.27$   & $(2)$  \\ 
 OH conjugate lines and radio lines & $z=0.765$&   $g_{\rm p}
\left({\frac{\alpha^2 m_{\rm e}}{m_{\rm p}}}\right)^{1.57}$ &$0.27\pm0.27$    & $(3)$  \\ 
 OH conjugate lines and radio lines & $z=0.685$&   $g_{\rm p}
\left({\frac{\alpha^2 m_{\rm e}}{m_{\rm p}}}\right)^{1.57}$&$0.11 \pm 0.13$     & $(3)$   \\ \hline
\end{tabular}}
\medskip
 Notes. The observational methods consist in comparing the redshift obtained with different spectral lines.  Columns: $(1)$ observational method specifying which lines are compared; $(2)$ redshift or redshift interval;  $(3)$ quantity measured; $(4)$ mean value of $\frac{\Delta \alpha}{\alpha}$ and its corresponding $1 \sigma$ error; $(5)$ reference. 
 References: (1) \citet{Tzana07}; (2) \citet{Murphy02}; (3) \citet{kanekar05}. 
\end{table}