In a study aimed at reducing developmental problems in low-birth-weight (under 2500 grams) babies (Journal of the American Medical Association, June 13, 1990, page 3040), 347 infants were exposed to a special educational curriculum while 561 did not receive any special help. After 3 years the children exposed to the special curriculum showed a mean IQ of 93.5 with a standard deviation of 19.1; the other children had a mean IQ of 84.5 with a standard deviation of 19.9. Find a 95% confidence interval estimate for the difference in mean IQs of low-birth-weight babies who receive special intervention and those who do not.
(A) (93.5-84.5) ± 1.97 v((19.1)2/347)+((19.9)2/561))
(B) (93.5-84.5) ± 1.97 ((19.1/v347)+(19.9/v561))
(C) (93.5-84.5) ± 1.65 v((19.1)2/347)+((19.1)2/561))
(D) (93.5-84.5) ± 1.65 ((19.1/v347)+(19.9/v561))
(E) (93.5-84.5) ± 1.65 v((19.1)2+(19.9)2)/(347+561))
Answer: A