\begin{tabular}{*{3}{l}}
\hline
                  & \multicolumn{2}{c}{M1}   \tabularnewline
                   &Estimate  &(S.E.)  \tabularnewline
 \hline
 \hline
   (Intercept)     &3.555   &   (4.459) \tabularnewline
   x1              &0.148   &   (0.160) \tabularnewline
   x2              &0.195   &   (0.155) \tabularnewline
 \hline
 N                 &100       &        \tabularnewline
 RMSE             &7.815         & \tabularnewline
 $R^2$             &0.135         & \tabularnewline
 adj $R^2$         &0.117         & \tabularnewline
 \hline
\hline
 
 \multicolumn{3}{c}{${*  p}\le 0.05$${*\!\!*  p}\le 0.01$${*\!\!*\!\!*  p}\le 0.001$}\tabularnewline
 \end{tabular}