由 自由度df决定的正偏态分布。

A positively skewed distribution determined by the degrees of freedom (df).

数值：X²都是正值。

可加性：几个X²的变量的和仍然服从卡方分布。

形状：

① 取决于类目数，而不是样本数。（df=C-1）

② 卡方分布呈现正偏态，右端无限延伸，不与基线相交。

③ df越大，分布越趋向对称，越趋向正态分布。

临界值：df增加，临界值增加

Numerical value: X² are positive.

Additivity：The sum of several X² variables still obeys a chi-square distribution.

Shape：

① Depends on the number of classes, not the number of samples.（df=C-1）

② The chi-square distribution exhibits a positive skewness with an infinite extension at the right end that does not intersect the baseline.

③ The larger df is, the more the distribution tends to be symmetric and normal.

Threshold value：Increasing df results in an increase in the critical value.