There's an appendix to one of the chapters in Jeremy Siegel's book where he says that one of the most important applications of this theory is to measure how successful an investor is.

刚才讲的是,杰里米·西格尔书上的附录,他认为这个理论最重要的应用,就是衡量一个投资者的收益

耶鲁公开课 - 金融市场课程节选

Now, underlying our theory is the idea that we measure the outcome of your investment in your portfolio by the mean of the return on the portfolio and the variance of the return on the portfolio.

而理论的基础是,我们通过计算,组合收益率的均值，和组合收益率的方差,来衡量一个投资组合的优劣。

耶鲁公开课 - 金融市场课程节选