\begin{tabular}{*{3}{l}}
 \hline
                &\multicolumn{2}{c}{M1}   \\
                &Estimate &(S.E.) \\
 \hline
 \hline
  (Intercept)    & -0.678  &   (4.345) \\
  x1             &  0.18*  &   (0.066) \\
  x2             &  0.229*  &   (0.069) \\
 \hline 
 N                &100      &       \\
 RMSE            &6.717        & \\
 $R^2$           &0.194        & \\
 adj $R^2$       &0.178        & \\
 \hline
 \hline
 
 \multicolumn{2}{l}{${*}  p \le 0.05$   }\\
 \end{tabular}