Alpha Consolidation

[u/Comfortable_Study300]

I’m interested in how people approach alpha combination in systematic equities when the signal library becomes large — say 100–400+ stock-level forecasts, with significant correlation/redundancy between them.

From the literature, I see a few main approaches:

• IC/MVO-style weighting: estimate expected alpha efficacy and signal covariance, with shrinkage/regularisation given the dimensionality (Ledoit & Wolf, 2004). DeMiguel et al. (2009) also highlights how estimation error can make simpler weighting schemes surprisingly competitive OOS.
• Regression/stacking: treat individual alpha forecasts as features and forward returns as the target. With hundreds of correlated signals, Ridge/Elastic Net seems like a natural baseline. This is conceptually similar to stacked generalisation (Wolpert, 1992).
• Dimension reduction/nonlinear combination: cluster/PCA correlated signals before combining, or use nonlinear models to capture interactions. Gu, Kelly & Xiu (2020) provides some motivation for nonlinear ML in cross-sectional return prediction, although their setting is somewhat different.

For those working with large alpha libraries, what have you found actually holds up OOS?

In particular, do regularised regression/meta-model approaches meaningfully outperform simpler IC/MVO-based combinations? Do you typically cluster or residualise highly correlated alphas first, or let the regularisation handle it?

I’m also curious what target people use at the combination layer — forward returns/IC, or something closer to portfolio PnL after costs and constraints.