In Exercise 9.26 on page 538 we consider separate simple linear models to predict NBA winning percentages using PtsFor and PtsAgainst. In Exercise 10.34 we combine these to form a multiple regression model. The data is in NBAStandings.
(a) Compare the percentages of variability in winning percentages that are explained by these three models (PtsFor alone, PtsAgainst alone, and the two together in a multiple regression).
(b) Create a new predictor, Diff = PtsFor − PtsAgainst, to measure the average margin of victory (or defeat) for each team. Use it as a single predictor in a simple linear model for WinPct. Include a scatterplot with the regression
line.

Exercise 9.26 on page 538

A common (and hotly debated) saying among sports fans is ‘‘Defense wins championships.’’ Is offensive scoring ability or defensive stinginess a better indicator of a team’s success? To investigate this question we’ll use data from the 2010–11 National Basketball Association (NBA) regular season. The data stored in NBAStandings include each team’s record (wins, losses, and winning percentage) along with the average number of points the team scored per game (PtsFor) and average number of points scored against them (PtsAgainst).