Markets Becoming More Efficient: The Disappearing Index Effect
Greenwood and Sammon’s findings of a disappearing index effect provides further support for the findings of McLean and Pontiff, Does Academic Research Destroy Stock Return Predictability? 2016. Once anomalies are well recognized by the market they decline and may even disappear, though limits to arbitrage can allow them to persist. Their findings also provide support for Andrew Lo’s The Adaptive Markets Hypothesis (2004). The bottom line is that markets are becoming more efficient, raising the hurdles for active managers to generate alpha.