Scarle · 2022年09月14日
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.
为什么cov大于零cor就一定大于零
NO.PZ2021061603000034 问题如下 Consir two variables, A anIf variable A ha meof-0.56, variable B ha meof 0.23, anthe covarianbetween the two variables is positive, the correlation between these two variables is: A.negative. B.zero. C.positive. C is correct. The correlation coefficient is positive because the covarianis positive. The fathone or both variables have a negative mees not affethe sign of the correlation coefficient. correlation =Sxy/(Sx*Sy),然后题目说的covarian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？
NO.PZ2021061603000034 问题如下 Consir two variables, A anIf variable A ha meof-0.56, variable B ha meof 0.23, anthe covarianbetween the two variables is positive, the correlation between these two variables is: A.negative. B.zero. C.positive. C is correct. The correlation coefficient is positive because the covarianis positive. The fathone or both variables have a negative mees not affethe sign of the correlation coefficient. No.PZ2021061603000034 (选择题)来源: 原版书Consir two variables, A anIf variable A ha meof-0.56, variable B ha meof 0.23, anthe covarianbetween the two variables is positive, the correlation between these two variables is:您的回答正确答案是: CAnegative.Bzero.Cpositive.求助老师
NO.PZ2021061603000034 问题如下 Consir two variables, A anIf variable A ha meof-0.56, variable B ha meof 0.23, anthe covarianbetween the two variables is positive, the correlation between these two variables is: A.negative. B.zero. C.positive. C is correct. The correlation coefficient is positive because the covarianis positive. The fathone or both variables have a negative mees not affethe sign of the correlation coefficient. 根据公式 R=S/两个标准差的乘积， S是positive 那就是正号 ，标准差一正一负，然后相除以后得到CORRELATION,就是负的 所以是negative ,哪里理解错了？
NO.PZ2021061603000034 这道题中mean这个条件有什么作用？还有一个不理解的就是，covariance大于0推出correlation也大于0是如何得到的呢？correlation不是由covariance除以两个变量的标准差得到的么？这道题的逻辑怎么给他理顺？求助一下，谢谢
