以下是引用chenholan在2009-11-5 6:48:00的发言：
standard deviation标准差
1 standard deviations from the mean就是mean+standard deviation
2.5 standard deviations from the mean就是mean+2.5standard deviation
不在这个范围的（就是大于+2.5，小于-2.5）就是大于2.5 standard deviations from the mean。
agree | 
