关于PE 是否有diversification的优点。

原版书分别在两个部分提到了PE的相关性，一是在historical performance知识点下，二是在roles in the portfolio下。这两处说法就有不一致的地方。

historical performance: 

Private equity returns have exhibited a low correlation with the returns to publicly traded securities, making private equity an attractive
addition to a portfolio. However, because of a lack of observable market prices for private equity, short-term return and correlation data
may be subject to the smoothing effects of stale prices.

Roles in portfolio:

The moderately high average correlation of private equity returns with publicly traded share returns that has been documented has a plausible economic explanation: All types of businesses have some exposure to economic and industry conditions, so correlations between public and private equity returns may be expected to be positive. Furthermore, venture capital uses public equity markets as one main exit route, so returns to VC fund investors can be expected to be higher when public equity market values are advancing. 

Private equity probably can play a moderate role as a risk diversifier. However, many investors look to private equity investment for long-term return enhancement.

所以不要关注historical performance那里，重点还是要掌握roles in portfolio这个知识点下的内容。