7.42 Babies. Is the gestational age (time between conception and birth) of a low birth-weight baby useful in predicting head circumference at birth? Twenty-ve low birth-weight babies were studied at a Harvard teaching hospital; the investigators calculated the regression of head circum- ference (measured in centimeters) against gestational age (measured in weeks). The estimated regression line is

head circumference = 3.91 + 0.78 x gestational age

(a) What is the predicted head circumference for a baby whose gestational age is 28 weeks?

(b) The standard error for the coecient of gestational age is 0.35, which is associated with df = 23. Does the model provide strong evidence that gestational age is signicantly associated with head circumference?

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