Warren Buffett is a long-term investor, but is required by law to disclose his trades on a quarterly basis. The market seems to under-react to the revelation of his trades. From 1980 to 2006, it has been possible to achieve investment results similar to Buffett's own simply by following his...

We study effects of correlation ambiguity on portfolio choice when the number of risky assets is large. We find that the optimal portfolio contains only a fraction of available risky assets. With 100 stocks randomly selected from the S&P 500, less than 20 stocks will be held in the optimal...