One more thing, I said they're not independent, so we have to talk about the covariance between the returns.

还有，我说过它们不是相互独立的，因此我们还需要讨论两个收益率的协方差。

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If you get a lot of negative products, that makes the covariance negative.

很多个负值的结果相加,就会使协方差是一个负值

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A negative covariance means that they tend to move opposite each other.

负值的协方差就表示,二者反向变动

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Covariance is a measure of how much two variables move together.

协方差衡量的是两个变量一起变动的情况

耶鲁公开课 - 金融市场课程节选

A positive covariance means that the two move together.

一个正值的协方差表示两个变量同向变动

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Another concept that's very basic here is covariance.

另一个基本的概念是协方差

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So this is a measure--it's a scaled covariance.

这个指标是相关系数

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I computed the returns on the stocks, bonds, and oil for every year from 1983 and I computed the average returns, which I take as the expected returns, I took the standard deviations, and I took the covariance.

我计算了从1983年以来每年的股票,债券和石油的收益，从而得出平均收益率，这些平均收益率作为预期收益率，然后算得标准差及协方差。

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Covariance is--we'll call it--now we have two random variables, so cov... I'll just talk about it in a sample term.

协方差是...我们有两个随机变量,x和y的协方差是,从样本的角度来说

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So, the higher the covariance is, generally, the higher--you can see from here-- 2 of the portfolio.

所以总的来说，你可以从这里看出，协方差越大-,投资组合的σ2越高，the，higher，the，σ

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If they tend to move together, when x is high and y is high together at the same time, then the covariance will tend to be a positive number.

如果x和y同向变动,当x值和y值同时都很大,协方差的结果将会是一个正值

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