CHALLENGE Running and heart rate. How does regular running affect heart rate? The RUNNERS data set, described in detail in the Data Appendix, contains heart rates for four groups of people:

Sedentary females Sedentary males Female runners (at least 15 miles per week)

Male runners (at least 15 miles per week)

The heart rates were measured after 6 minutes of exercise on a treadmill. There are 200 subjects in each group. Give a complete comparison of the four distributions, using both graphs and numerical summaries. How would you describe the effect of running on heart rate? Is the effect different for men and women?

The WORKERS data set, described in the Data Appendix, contains the sex, level of education, and income of 71,076 people between the ages of 25 and 64 who were employed full-time in 2001.

The boxplots in Figure 1.23 compare the distributions of income for people with five levels of education. This figure is a variation on the boxplot idea: because large data sets often contain very extreme observations, the lines extend from the central box only to the 5th and 95th percentiles.

Exercises 1.82 to 1.84 concern these data.

50 0

100 150 200 250 300 Not HS grad HS grad Some college Bachelor’s Advanced Total income (thousands of dollars)

FIGURE 1.23 Boxplots comparing the distributions of income for employed people aged 25 to 64 years with five different levels of education. The lines extend from the quartiles to the 5th and 95th percentiles.