\begin{table}[htbp]
\centering
\begin{threeparttable}
\caption{HAR-RV Model Estimates}
\label{tab:har_rv}
\begin{tabular}{l S l S}
\toprule
Variable & {Coefficient} & (Std Err) & {$t$-stat} \\
\midrule
    const & 0.0121 & (0.0081) & 1.50 \\
    rv\_d & 0.0082 & (0.1130) & 0.07 \\
    rv\_w & 0.1432 & (0.1079) & 1.33 \\
    rv\_m & 0.0299 & (0.0373) & 0.80 \\
\midrule
    $R^2$ & \multicolumn{3}{c}{0.106} \\
    Adj.~$R^2$ & \multicolumn{3}{c}{0.083} \\
\bottomrule
\end{tabular}
\begin{tablenotes}
\small
\item \textit{Notes:} HAR-RV model following \citet{corsi2009simple}.
RV$_{t+1}^{(d)} = c + \beta_d RV_t^{(d)} + \beta_w RV_t^{(w)} + \beta_m RV_t^{(m)} + \varepsilon_{t+1}$.
Newey--West standard errors with 5 lags.
\end{tablenotes}
\end{threeparttable}
\end{table}