统计的核心是均值与方差。不论我们使用什么统计方法，对现象进行统计分析时，实际上都是在它们的平均数和标准差上做文章。因为平均数和标准差是现象变化的统计规律的两个方面。平均数反映的是现象的集中趋势，是现象的一致性结果；而标准差是现象的离中趋势，反映现象差异性 The core of statistics is the mean and variance. No matter what statistical methods we use, the statistical analysis of phenomena is actually an issue in terms of their mean and standard deviation. Because the mean and standard deviation are two aspects of the statistical law of the phenomenon of change. The average reflects the concentration of the phenomenon of the phenomenon is the phenomenon of the consistency of the results; and standard deviation is the phenomenon of the trend from the center to reflect the phenomenon of differences