44. Designated hitter 2009. American League baseball teams play their games with the designated hitter rule, meaning that pitchers do not bat. The league believes that replacing the pitcher, traditionally a weak hitter, with another player in the batting order produces more runs and generates more interest among fans. The data provided in the file on the CD include the average numbers of runs scored per game (Runs per game) by American League and National League teams for the 2009 season (http://espn.go.

com/mlb/stats/team/_/stat/batting/year/2009).

a) Create an appropriate display of these data. What do you see?

b) With a 95% confidence interval, estimate the mean number of runs scored by American League teams.

c) With a 95% confidence interval, estimate the mean number of runs scored by National League teams.

d) Explain why you should not use two separate confidence intervals to decide whether the two leagues differ in average number of runs scored.