\begin{table}%t3
%\centering
\par
\caption{The probability of a false rejection of the null hypothesis
that the sample and the
  reference populations have equal means, according to the Single-Sample Sign
  test $S_{\rm{s}}$, the $t$-test $S_{\rm{t}}$ and the Wilcoxon Rank Sum test $S_{\rm{W}}$.
  The corresponding values of $a$, $t$ and~$z$ are given in brackets. \label{Tab:test}}
\begin{tabular}{cccc}
\hline \hline
& minimum & mid-decl & maximum\\
\hline\\[-3mm]
daily $R_{\rm{g}}$ & $10\pm12.3$&$55\pm34$&$115\pm 48$\\
$S_{\rm{s}}\ (a)$ & 0.85 (0.18) & 0.05 ($-2$) & 0.03 ($-2.3$)\\
$S_{\rm{t}}\ (t)$ & 0.16\ (1.5) & $0.0043\ (-3.4)$& $10^{-6}\ (-8.6)$\\
$S_{\rm{W}}\ (z)$& 0.28 ($-0.58$)  & $3\cdot 10^{-5}$ (4)  & 0 (5.7) \\[1mm]\hline\\[-3mm]
monthly $R_{\rm{g}}$ & $10\pm8.3$&$55\pm27$&$115\pm 39$\\
$S_{\rm{t}}\ (t)$ & 0.03 (2.6) & $10^{-10}$ ($-14$)& 0.0 ($-27$)\\
$S_{\rm{W}}\ (z)$ & 0.18 (0.88) & $10^{-5}$ (4.2)& 0.0 (5.7)\\
\hline
\end{tabular}
\end{table}