参数假设检验：对差异进行定量的分析，确定其性质，是随机误差还是系统误差.为给出两者界限，找一检验统计量T，在H0成立下其分布已知。-Parameter hypothesis test: a quantitative analysis of the differences, to determine its nature, is random error or system error. Is given two boundaries, looking for a test statistic T