The Illusory Nature of Momentum Profits

In markets with trading friction, the incorporation of information into market prices can be substantially delayed through a weakening of the arbitrage process. We re-examine the profitability of relative-strength, or momentum, trading strategies (buying past strong performers and selling past weak performers). We find that standard relative-strength strategies require frequent trading in disproportionately high-cost securities so that trading costs prevent profitable strategy execution. In the cross section, we find that those stocks that generate large momentum returns are precisely those stocks with high trading costs. We conclude that the magnitude of the abnormal returns associated with these trading strategies creates an illusion of profit opportunity when, in fact, none exists.