说明：  不同于点估计，点估计出来的是一个值，而区间估计估计出来的是一个区间。这里不得不说一下枢轴变量了，枢轴变量里面只有一个待估计的位置参数，这个枢轴变量一般都服从某个分布，比如说正太分布，T分布，那么我们可以定义一个a，然后在置信水平在1-a下，求出相应的置信区间。总之枢轴变量真的很重要。
(Unlike point estimation, point estimation yields a value, while interval estimation yields an interval. There is only one position parameter to be estimated in the pivot variable. This pivot variable generally obeys a certain distribution, such as orthodox distribution, T distribution. Then we can define an a, and then at the confidence level of 1-a, we can find the corresponding confidence interval. In short, pivot variables are really important.)