Structural Benchmark Drift and Hidden Peer Risk: Governance Implications for Active Equity Management

Benchmark indexes define investment mandates and anchor performance evaluation in active equity management, yet actual portfolio exposures may deviate systematically from those definitions. Using 4,592 global equity funds across 10 benchmark categories from 2015 to 2024, the authors document pervasive co-movement in active returns: up to 90% of funds exhibit positive beta relative to their peer group’s average performance. Regression results show that funds exhibit economically significant off-benchmark exposures across size, style, and region dimensions. Large-cap funds load on small-cap factors; small-cap funds retain exposure to larger stocks; developed-market funds hold emerging-market exposure; and international mandates exhibit systematic growth tilts. Tracking error is strongly associated with these structural tilts: high-active-risk funds display the most pronounced benchmark drift, while low-active-risk funds remain closer to index definitions. These findings indicate that benchmark categories overstate the purity of delivered exposures and that peer clustering reduces the diversification benefits of combining multiple managers within the same mandate. Effective governance requires distinguishing structural beta positioning from true alpha generation.