样品均值和样品标准偏差(S)是两个既重要又常用的特征量。样品均值表示数据的分布中心,即数据的重心位置,以代表总体的平均水平,用表示。若以Xi(i=1,2,…,n)表示从总体中抽取一批样品得到的数据,n为样品数,则样品均值的定义式为 Sample mean  and sample standard deviation (S) are two important and commonly used features. The sample mean represents the center of distribution of the data, the center of gravity of the data, to represent the overall average level, expressed as . If Xi (i = 1,2, ..., n) represents the data obtained from the bulk of a sample, n is the number of samples, the sample mean is defined as