Normal Probability Plots|outlier

6.4 Assessing normality; normal Probability Plots

The normal probability plot is a graphical technique to identify substantive departures from normality

 

 

 

即如果sample满足正态分布，则1-12位置上对应的y值应该为这一列上的值

Noted：

之前统计正态分布时需要由直方图过渡到正态曲线，横坐标是每一类，在这里是样本本身。

 

 

 

由table3一一对应，作图：

 

 

根据以上rule判断正态情况。

Note: If two or more observations in a sample are equal,you can think of them as slightly different from one another for purposes of obtaining their normal scores.

 

 

如图，可将normal-score值改为对应的percentage

A probability or percent scale is used instead of normal scores

Detecting Outliers with normal Probability Plots

 

 

a去掉outlier得到b

 

 

由此判断该数据为正态分布