If you're comparing two portfolios with the same expected return, then you want the one with the lower variance.

比较两个有相同预期收益率的投资组合时，你会选择方差小的那一个。

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It shows the standard deviation of the return on the portfolio as a function of the expected return on the portfolio.

它是投资组合的收益标准差,关于预期收益率的函数图像。

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2% You could say, I think my portfolio has an expected return of 12%-- that would be better than if it had an expected return of 10%.

如果一个投资组合的预期收益率有-,那就比一个只有10%的投资组合要好。

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Last year the return on the Yale portfolio was 28% in one year.

去年耶鲁大学投资组合的收益率,是28%

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The return, of course, in any given time period is the percentage increase in the portfolio; or, it could be a negative number, it could be a decrease.

当然了，收益率是一定时间内,投资组合的增长率;,也可能是一个负数，表示负增长。

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Over this time period, that portfolio had an expected return of something like a little over 9% and it had a standard deviation of a little over 9%.

在这个时间段，这个投资组合的预期收益率是,9%多一点%,标准差是9%多一点。

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But ultimately, everyone agrees I-- that's the premise here, that for the-- if you're comparing two portfolios with the same variance, then you want the one with the higher expected return.

但归根结底大家都会同意这一点-,这是一个前提-,当你比较两个有相同方差的投资组合时，你会选择预期收益率高的那一个。

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Then, once we did that we could plug that into the formula that I gave you last time and get the standard deviation of the portfolio and the expected return on the portfolio.

再将估算出的数值代入到,上节课给你们的公式中,就能得到资产投资组合的标准差,和该投资组合的预期收益率

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What is the portfolio expected return?

投资组合的预期收益率是什么？

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Over the past twenty years, we've generated 15.6% per annum return, but that headline number obviously has a lot to do with the equity orientationof the portfolio but doesn't describe the importance of the diversification.

过去20年间,我们的年收益率达到15.6%,虽然媒体头条报道这一收益率,总强调与投资组合的股权导向有很大关系,但没有描述出投资多元化的重要性

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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。

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So, the optimal thing to do if you live in a world like this n is to get n as large possible and you can reduce the standard deviation of the portfolio very much and there's no cost in terms of expected return.

如果现实中也这样简单的话,那么你就尽量增大,这样就能让投资组合的标准差,就会大大降低,从预期收益率的角度来看,这样做的成本是零。

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