\renewcommand\cellalign{t}
\begin{threeparttable}
\begin{tabular}{lcc}
\toprule
 & \multicolumn{2}{c}{Y} \\
\cmidrule(lr){2-3}
 & (1) & (2) \\
\midrule
X1 & \makecell{-0.950*** \\ (0.067)} & \makecell{0.004 \\ (0.033)} \\
X2 & \makecell{-0.174*** \\ (0.018)} & \makecell{-0.014 \\ (0.011)} \\
f2 &  & \makecell{0.003 \\ (0.004)} \\
\midrule
f1 & x & x \\
\midrule
Observations & 1994 & 997 \\
S.E. type & by: f1 & by: f1+f2 \\
$R^2$ & 0.489 & - \\
\bottomrule
\end{tabular}
\footnotesize Significance levels: $*$ p $<$ 0.05, $**$ p $<$ 0.01, $***$ p $<$ 0.001. Format of coefficient cell: Coefficient
 (Std. Error)
\end{threeparttable}
