We propose a rational theory of momentum and reversal based on delegated portfolio management. Flows between investment funds are triggered by changes in fund managers’ efficiency, which investors either observe directly or infer from past performance. Momentum arises if fund flows exhibit inertia, and because rational prices do not fully adjust to reflect future flows. Reversal arises because flows push prices away from fundamental values. Besides momentum and reversal, fund flows generate comovement, lead-lag effects and amplification, with all effects being larger for assets with high idiosyncratic risk. Managers’ concern with commercial risk can make prices more volatile.
This is a revised version of Working Paper Series No 2, FMG Discussion Paper No 621.
