=+5.21 ● ▼ The accompanying data on x 5 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 5 volume of cerebral grey matter (in ml) at age 2 to 5 years were read from a graph in the article described in the chapter introduction (Journal of the American Medical Association [2003]).

Head CircumferCerebral Grey ence z Scores at Matter (ml) 2–5 yr 6–14 Months 680 2.75 690 1.2 700 2.3 720 .25 740 .3 740 1.5 750 1.1 750 2.0 760 1.1 780 1.1 790 2.0 810 2.1 815 2.8 820 2.2 825 .9 835 2.35 840 2.3 845 2.2