11. Confidence Interval for Effect of Birth Weight on IQ Score When investigating a relationship between birth weight and IQ, researchers found that 258 subjects with extremely low birth weights (less than 1000 g) had Wechsler IQ scores at age 8 with a mean of 95.5 and a standard deviation of 16.0. For 220 subjects with normal birth weights, the mean at age 8 is 104.9 and the standard deviation is 14.1. (Based on data

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480 Chapter 9 Inferences from Two Samples from “Neurobehavioral Outcomes of School-age Children Born Extremely Low Birth Weight or Very Preterm in the 1990s,” by Anderson et al., Journal of the American Medical Association, Vol. 289, No. 24.) Construct a 95% confidence interval estimate of the difference between the mean IQ score of 8-year-old children born with low birth weight and the mean of 8-year-old children born with normal birth weight. Does IQ score appear to be affected by birth weight?