\begin{tabular}{l d d d d d d}
\toprule
 & \multicolumn{1}{c}{$\hat{\mathbf b}_k$}
 & \multicolumn{3}{c}{Écart-type estimé}
 & \multicolumn{2}{c}{Student}\\
\cmidrule(lr){3-5}\cmidrule(lr){6-7}
 &
 & \multicolumn{1}{c}{usuel}
 & \multicolumn{1}{c}{HC1}
 & \multicolumn{1}{c}{HC3}
 & \multicolumn{1}{c}{usuel}
 & \multicolumn{1}{c}{HC3}\\
\midrule
Constante & 0.1280 & 0.1059 & 0.1071 & 0.1084 & 1.21 & 1.18\\
$educ$ & 0.0904 & 0.0075 & 0.0078 & 0.0079 & 12.10 & 11.45\\
$exper$ & 0.0410 & 0.0052 & 0.0050 & 0.0051 & 7.89 & 8.12\\
$exper^2/100$ & -0.0714 & 0.0116 & 0.0110 & 0.0111 & -6.16 & -6.45\\
\bottomrule
\end{tabular}