Many of the most effective statistical studies are comparative. We may wish to compare customer satisfaction of men and women who use an online fantasy football site or compare perceptions of sales careers between business students in the United States, Canada, and China. Companies use comparative studies to develop better products and to determine how best to reach their target audience. Here are some examples.
With a quantitative response, we display these comparisons with back-to-back stemplots or side-by-side boxplots and histograms, and we measure them with five-number summaries or with means and standard deviations.
When only two groups are compared, Chapter 7 provides the tools we need to answer the question, “Is the difference between groups statistically significant?” Two-sample t procedures compare the means of the two populations and are sufficiently robust to be widely useful. In this chapter, we compare any number of means by techniques that generalize the two-sample t methods and share its robustness and usefulness.