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SYc · 2023年12月05日

没明白这个题

NO.PZ2021061603000034

问题如下:

Consider two variables, A and B. If variable A has a mean of-0.56, variable B has a mean of 0.23, and the covariance between the two variables is positive, the correlation between these two variables is:

选项:

A.negative. B.zero. C.positive.

解释:

C is correct.

The correlation coefficient is positive because the covariance is positive. The fact that one or both variables have a negative mean does not affect the sign of the correlation coefficient.

correlation =Sxy/(Sx*Sy),然后题目说的covariance 方差永远都是positive ,题目强调positive 有什么意义呢?所以Sx和Sy有可能一正一负啊。是怎么退出正确答案的?

1 个答案

品职助教_七七 · 2023年12月06日

嗨,从没放弃的小努力你好:


标准差为方差开根号后取正值,不会是负值。所以,correlation的符号完全取决于公式分子上的covariance。本题covariance为正,correlation就也一定是正值。

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