[讨论]卡方检验

卡方检验的目的：

２变数间的比较：判定行变数间・列变数之间是否存在一定关系的检验手法。
x2检验（chi-square test）或称卡方检验，是一种用途较广的假设检验方法。可以分为成组比较（不配对资料）和个别比较（配对，或同一对象两种处理的比较）两类。
在用Minitab进行卡方检验的时候，有一句“2 cells with expected counts less than 5”，这么一句话，可是对这句话一直不是很了解，看了帮助文件中关于相关内容的解释：
Cells with Small Expected Frequencies    
Minitab displays the number of cells that have expected frequencies less than 5. In Example of Chi-Square, there were 2 such cells. Some statisticians hesitate to use the c test if more than 20% of the cells have expected frequencies below five, especially if the p-value is small and these cells give a large contribution to the total c value.
If any cell has an expected frequency less than one, the total c is not displayed, because the results may not be valid. If some cells have small expected frequencies, consider combining or omitting row and/or column categories.
还是不是很理解，希望大家多多指教！！！！