Most commonly, we wish to know if the average (mean) of the continuous variable differs
across the categories. For this reason, we often call these techniques “comparison
of means.”
Now, we have already looked into this question of whether a mean of a variable differs
across groups. You will find such an analysis in Chapter 8, where we get descriptive
statistics of a variable across categories. This chapter takes this analysis further,
however, by testing whether any difference in means between categories is statistically significant, which is a question we did not ask previously.
For instance, in Chapter 8, we looked at whether Sales (the dependent variable in
the main textbook example) differs significantly across License categories (Freeware
vs Premium). We will now analyze these differences in averages by asking whether the
difference is statistically significantly different from zero.