\begin{tabular}{l c cc cc c cc cc}
\toprule
 & & \multicolumn{4}{c}{Random holdout} & & \multicolumn{4}{c}{Forward-in-time holdout} \\
\cmidrule{3-6}\cmidrule{8-11}
 & & \multicolumn{2}{c}{MdAPE (\%)} & \multicolumn{2}{c}{$R^2_{\ln}$} & & \multicolumn{2}{c}{MdAPE (\%)} & \multicolumn{2}{c}{$R^2_{\ln}$} \\
\cmidrule{3-4}\cmidrule{5-6}\cmidrule{8-9}\cmidrule{10-11}
Model & $\hat{s}$ & Median & Mean & Median & Mean & & Median & Mean & Median & Mean \\
\midrule
A2 Semi-log & 1.070 & 19.0 & 18.2 & 0.546 & 0.533 & & 23.2 & 20.6 & 0.426 & 0.458 \\
A3 Log-log & 1.064 & 18.0 & 17.0 & 0.580 & 0.569 & & 21.8 & 19.2 & 0.481 & 0.513 \\
A4 Box--Cox & --- & 18.6 & 17.9 & 0.548 & 0.536 & & 21.0 & 19.6 & 0.476 & 0.490 \\
A5 Quadratics & 1.070 & 19.2 & 18.1 & 0.546 & 0.533 & & 23.3 & 20.5 & 0.442 & 0.479 \\
A6 Splines & 1.062 & 17.6 & 16.5 & 0.590 & 0.579 & & 21.7 & 19.1 & 0.491 & 0.522 \\
D2 Ridge & 1.063 & 17.7 & 16.7 & 0.587 & 0.577 & & 22.3 & 19.5 & 0.480 & 0.515 \\
D3 Random forest & 1.032 & 14.6 & 13.7 & 0.631 & 0.629 & & 21.3 & 19.4 & 0.519 & 0.544 \\
D4 Boosting & 1.048 & 14.4 & 13.1 & 0.642 & 0.636 & & 21.2 & 18.4 & 0.521 & 0.556 \\
\bottomrule
\end{tabular}