A portfolio manager gathers monthly stock returns going back to the year 1901 and estimates mean returns, variances, and cross-market correlations for 50 countries. She identifies the efficient frontier and then invests in the portfolio that is mean-variance efficient relative to the U.S. risk-free rate. Is this fund manager's performance over the coming year likely to be similar to the historical record? Over the next five years? Over the next ten years? Explain.