Let's compare the average miles per gallon (mpg) among the cars in the different repair groups using Analysis of Variance. You might think to use proc anova for such an analysis, but proc anova assumes that the sample sizes for all groups are equal, an assumption that is frequently untrue.   Instead, we will use proc glm to perform an ANOVA comparing the prices among the repair groups.  Since there are so few cars with a repair record (rep78) of 1 or 2, we will use a where statement to omit them, allowing us to concentrate on the cars with repair records of 3, 4 and 5.  The proc glm below performs an Analysis of Variance testing whether the average mpg for the 3 repair groups (rep78) are the same.  It also produces the means for the 3 repair groups。
红色的字说是假定样本量要相同，但是很多人都没有这么做，这是为什么呢？