\begin{table}[htbp]\centering
\def\sym#1{\ifmmode^{#1}\else\(^{#1}\)\fi}
\caption{Subgroup Effects: Sociocultural Variables \label{tab:union}}
\begin{tabular}{l*{2}{c}}
\hline\hline
                    &\multicolumn{1}{c}{(1)}&\multicolumn{1}{c}{(2)}\\
                    &\multicolumn{1}{c}{Base}&\multicolumn{1}{c}{Full}\\
                    &        b/se         &        b/se         \\
\hline
Treatment $\times$ Exports $\times$ Union Member&     -38.028         &     -28.589         \\
                    &    (21.651)         &    (20.243)         \\
Treatment $\times$ Imports $\times$ Union Member&       1.508         &       1.770         \\
                    &    (23.567)         &    (23.455)         \\
Treatment $\times$ Non-traded $\times$ Union Member&     -10.745         &      -0.899         \\
                    &    (18.228)         &    (17.202)         \\
\hline
N                   &        2406         &        2273         \\
r2                  &       0.074         &       0.095         \\
\hline\hline
\multicolumn{3}{l}{\footnotesize \sym{*} \(p<0.05\), \sym{**} \(p<0.01\), \sym{***} \(p<0.001\)}\\
\end{tabular}
\end{table}
