The accompanying data on x = head circumference z score (a comparison score with peers of the same age€”a positive score suggests a larger size than for peers) at age 6 to 14 months and y = volume of cerebral grey matter (in ml) at age 2 to = years were read from a graph in the article described in the chapter introduction (Journal of the American Medical Association [2003]).

a. Construct a scatterplot for these data.
b. What is the value of the correlation coef fi cient?
c. Find the equation of the least-squares line.
d. Predict the volume of cerebral grey matter at age 2 to = years for a child whose head circumference z score at age 12 months was 1.8.
e. Explain why it would not be a good idea to use the least-squares line to predict the volume of grey matter for a child whose head circumference z score was 3.0.

Cerebral Grey Matter (ml) 2-5 yr Head Circumference z Scores at 6-14 Months 1.2 .25 .3 2.35