The data in the accompanying table is from the paper “Six-Minute Walk Test in Children and Adolescents” (The Journal of Pediatrics [2007]: 395–399).

Two hundred and eighty boys completed a test that measures the distance that the subject can walk on a flat, hard surface in 6 minutes. For each age group shown in the table, the median distance walked by the boys in that age group is also given.

Age Group Representative Age (Midpoint of Age Group)

Median Six-minute Walk Distance

(meters)

3–5 4 544.3 6–8 7 584.0 9–11 10 667.3 12–15 13.5 701.1 16–18 17 727.6

a. With x 5 representative age and y 5 median distance walked in 6 minutes, construct a scatterplot.

Does the pattern in the scatterplot look linear?

b. Find the equation of the least-squares regression line that describes the relationship between median distance walked in 6 minutes and representative age.

c. Compute the five residuals and construct a residual plot. Are there any unusual features in the plot?