12. The article Measuring the Exposure of Infants to Tobacco Smoke (New Engl. J. Med., 1984: 1075—

1078) reports on a study in which various measurements were taken both from a random sample of infants who had been exposed to household smoke and from a sample of unexposed infants. The accompanying data consists of observations on urinary concentration of cotinine, a major metabolite of nicotine (the values constitute a subset of the original data and were read from a plot that appeared in the article). Does the data suggest that true average cotinine level is higher in exposed infants than in unexposed infants by more than 25? Carry out a test at signi cance level .05.

Unexposed 8 11 12 14 20 43 111 Exposed 35 56 83 92 128 150 176 208