Using data on international equity portfolio allocations by U.S. mutual funds, we estimate a portfolio expression derived from a standard mean-variance portfolio model extended with portfolio frictions. The optimal portfolio depends on the previous month and the buy-and-hold portfolio shares, and a present discounted value of expected excess returns. We estimate expected return differentials and use them in the portfolio regressions. The estimates imply significant portfolio frictions and a modest rate of risk aversion. While mutual fund portfolios significantly respond to expected returns, portfolio frictions lead to a weaker and a more gradual portfolio response to changes in expected returns.

We introduce a portfolio friction in a two-country DSGE model where investors face a constant probability to make new portfolio decisions. The friction leads to a more gradual portfolio adjustment to shocks and a weaker portfolio response to changes in expected excess returns. We apply the model to monthly data for the US and the rest of the world for equity portfolios. We show that the model is consistent with a broad set of evidence related to portfolios, equity prices, and excess returns for an intermediate level of friction. The evidence includes portfolio inertia, limited sensitivity to expected excess returns, a significant impact of financial shocks, excess return predictability, and asset price momentum and reversal.