Naive Diversification
研究发现，不完全分散的投资组合所需的超额回报仅取决于两个参数：股票风险溢价和股票收益之间的平均相关性。
Some diversifiable risk is always left in a portfolio. The argument here is that the excess risk in a randomly selected portfolio of a given size should be compensated for. The analysis shows that the required excess return of an imperfectly diversified portfolio depends on just two parameters: the equity risk premium and the average correlation between stock returns.