NO.PZ2022123001000128
问题如下：
Which of the following statements is correct regarding the chi-square test of independence?
选项：
A.The test has a one-sided rejection region
B.The null hypothesis is that the two groups are dependent
C.If there are two categories, each with three levels or groups, there are six degrees of freedom.
解释：
The test statistic comprises squared differences between the observed and expected values, so the test involves only one side, the right side. B is incorrect because the null hypothesis is that the groups are independent, and C is incorrect because with three levels of groups for the two categorical variables, there are four degrees of freedom.
每个分类各有三个子分类对应三行（r=3）和三列（c=3）正确的自由度应为（r-1）*（c-1）=（3-1）*（3-1）=4。
C的英文表述是什么意思？C选项说2个categories，有3个level，为什么自由度不是1*2？这个英文描述能不能请老师举个例子帮忙理解一下为什么是3行3列。谢谢
