Ages of couples 2007, part 2. Has the trend of decreasing difference in age at first marriage seen in Exercise 40 gotten stronger recently? Here are the scatterplot and residual plot for the data from 1975 through 2007, along with a regression for just those years.
a) Why is R2 higher for the first model (in Exercise 40)?
b) Is this linear model appropriate for the post-1975 data? Explain.
c) What does the slope say about marriage ages since 1975?
d) Explain why it's not safe to interpret the y-intercept.