143 Passive exposure to smoke. Passive exposure to environmental tobacco smoke has been associated with suppression of growth and an increased frequency of respiratory tract infections in normal children. Is this association more pronounced in children with cystic fibrosis? To answer this question, 43 children (18 girls and 25 boys)

attending a two-week summer camp for cystic fibrosis

patients were studied ( New England Journal of Medicine , Sept. 20, 1990). Researchers investigated the correlation between a child’s weight percentile ( y ) and the number of cigarettes smoked per day in the child’s home ( x ). The table on page 707 (saved in the CFSMOKE file) lists the data on the 25 boys. Using simple linear regression, the researchers predicted the weight percentile for the last observation ( x = 44 cigarettes) to be yn = 29.63. Given that the standard deviation of the model is s = 24.68, is this observation an outlier? Explain.

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No. of Cigarettes Smoked No. of Cigarettes Smoked Weight Percentile y per Day x Weight Percentile y per Day x 6 128 6 40 11 17 24 25 17 25 25 31 35 SREBROWLERSHO 0 15 23 20 7 998948 43 0 0 50 0 22 46 30 54 0 58 0 0 25 20 15 23 48383 62 0 66 0 66 23 0 87 44 10 Based on Rubin, B. K. "Exposure of children with cystic fibrosis to environmen- tal tobacco smoke." The New England Journal of Medicine, Sept. 20, 1990. Vol. 323, No. 12, p. 85 (data extracted from Figure 3).