The paper referenced in the previous exercise also gave the 6 minute walk distances for 248 girls ages 3 to 18 years. The median distances for the five age groups were
492.4 578.3 655.8 657.6 660.9
a. With x = representative age and y = median distance walked in 6 minutes, construct a scatterplot. How does the pattern for girls differ from the pattern for boys from Exercise 4.42?
b. Find the equation of the least squares regression line that describes the relationship between median distance walked in 6 minutes and representative age for girls.
c. Compute the five residuals and construct a residual plot. The authors of the paper decided to use a curve rather than a straight line to describe the relationship between median distance walked in 6 minutes and age for girls. What aspect of the residual plot supports this decision?