How Many Stocks Make a Diversified Portfolio?
发现，随机选股构建的分散化投资组合至少需要30只股票（借款投资者）或40只股票（贷款投资者），推翻了广为接受的10只股票即可充分分散的观点。
We show that a well-diversified portfolio of randomly chosen stocks must include at least 30 stocks for a borrowing investor and 40 stocks for a lending investor. This contradicts the widely accepted notion that the benefits of diversification are virtually exhausted when a portfolio contains approximately 10 stocks. We also contrast our result with the levels of diversification found in studies of individuals' portfolios.