\begin{tabular}{l cc c cc}
\toprule
 & \multicolumn{2}{c}{Random holdout} & & \multicolumn{2}{c}{Forward-in-time} \\
\cmidrule{2-3}\cmidrule{5-6}
Gradient-boosting configuration & MdAPE (\%) & $R^2_{\ln}$ & & MdAPE (\%) & $R^2_{\ln}$ \\
\midrule
Gradient boosting (baseline) & 14.4 & 0.642 & & 21.2 & 0.521 \\
Shallow (15 leaves, lr 0.05, 1500 iter) & 14.7 & 0.636 & & 21.4 & 0.521 \\
Deep (255 leaves, lr 0.05, 600 iter) & 14.3 & 0.645 & & 21.6 & 0.518 \\
Regularised (min leaf 200, L2 = 1) & 14.3 & 0.643 & & 21.5 & 0.522 \\
Early stopping on last 10\% of training months [700 / 1000 it.] & 14.5 & 0.641 & & 21.2 & 0.524 \\
\bottomrule
\end{tabular}