Peter · 2020年08月27日
问题如下：
Alice wants to research the variables X and Y, and the relationship between them. First, she chooses 150 samples and gets some summary statistics about these two variables. One of them is "Sum of cross-products of deviations from the mean", which is
=113.7384. What is the sample covariance?
选项：
A.0.7583
B.0.7633
C.0.7532
解释：
B is correct.
考点: Calculate and Interpret Correlation Coefficients.
解析: 变量X和Y的协方差计算如下：
=113.7384/149=0.7633
所以选择B选项。
想问一下这个在讲义的多少页。。完全没有印象了
NO.PZ2018101001000026 请问多元回归中，异方差、序列相关、多重共线性都不影响consistency. 请问是什么东西的consistency不受影响？谢谢！
NO.PZ2018101001000026 请问多元线性回归中coefficient是什么意思？coefficient estimate又是什么意思？谢谢！
是不是因为这里只有一个自变量，所以除以n-1。其实是n-k，k是自变量的个数。
0.7633 0.7532 B is correct. 考点: Calculate anInterpret Correlation Coefficients. 解析: 变量X和Y的协方差计算如下 Cov(X,Y)=∑i=1n(Xi−X‾)(Yi−Y‾)/(n−1)Cov{(X,Y)}=\sum_{i=1}^n{(X_i-\overline X)}{(Y_i-\overline Y)}/{(n-1)}Cov(X,Y)=∑i=1n(Xi−X)(Yi−Y)/(n−1)=113.7384/149=0.7633 所以选择B。老师一级讲义上协方差的公式没有要除以n或者n-1啊 这里解析里的公式为什么要除以
