按GB335 8 - 82《统计学名词及符号》的有关规定书写 ,常用如下 :(1)样本的算术平均数用英文小写x(中位数仍用M ) ;(2 )标准差用英文小写s ;(3)标准误用英文写sx;(4 )t检验用英文小写t ;(5 )F检验用英文大写F ;(6 )卡方检验用希文小写 χ2 ;(7)相关系数用英文小写r ;(8)自由度 According to the GB335 8 - 82 “statistical terms and symbols” of the relevant provisions of writing, commonly used as follows: (1) the arithmetic mean of the sample in English lowercase x (median still use M); (2) standard deviation in English lowercase s ; (3) standard misuse of English written sx; (4) t test in lowercase English t; (5) F test in uppercase F; (6) chi-square test Xi Xi lowercase χ2; (7) correlation coefficient in English Lowercase r; (8) degrees of freedom