The graph shows the ages of both men and women at first marriage (www.census.gov).

Clearly, the patterns for men and women are similar. But are the two lines getting closer together?
Here's a timeplot showing the difference in average age (men's age — women's age) at first marriage, the regression analysis, and the associated residuals plot.

Dependent variable is Age Difference
R-squared = 74.9% s = 0.2346
Variable Coefficient
Intercept ………………….. 32.968
Year ……………………… -0.01549
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.