Ages of couples, again. Has the trend of decreasing difference in age at first marriage seen in Exercise gotten stronger recently? Here are the scatterplot and residual plot for the data from 1975 through 2003, along with a regression for just those years.
a) Why is R2 higher for the first model (in Exercise)?
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 reasonable to interpret the y-intercept.
Exercise:
Ages of couples 2003. The graph shows the ages of both men and women at first marriage. (www.census. gov)
Clearly, the pattern for men is similar to the pattern for women. But are the two lines getting closer together?
Here's a time plot showing the difference in average age (men's age - women s age) at first marriage, the regression analysis, and the associated residuals plot.
a) What is the correlation between Age Difference and Year?
b) Interpret the slope of this line.
c) Predict the average age difference in 2015.
d) Describe reasons why you might not place much faith in that prediction.