Question 15.16
15.16 The 2008 and 2012 presidential elections. Democrat Barack Obama was elected president in 2008 and 2012. Figure 15.6 plots the percentage who voted for Obama in 2008 and 2012 for each of the 50 states and the District of Columbia.
(a) Describe in words the direction, form, and strength of the relationship between the percentage of votes for Obama in 2008 and the percentage in 2012. Are there any unusual features in the plot?
(b) The least-squares regression line is
Draw this line on a separate sheet of paper. (To draw the line, use the equation to predict for and for . Plot the two points and draw the line through them.)
(c) The correlation between these variables is . What percentage of the observed variation in 2012 percentages can be explained by straight-line dependence on 2008 percentages?
