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Genetic influences on cancer can be studied by manipulating the genetic makeup of mice

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Genetic influences on cancer can be studied by manipulating the genetic makeup of mice. One of the processes that turn genes on or off (so to speak) in particular locations is called "DNA methylation." Do low levels of this process help cause tumors? Compare mice altered to have low levels of DNA methylation with normal mice. Of 33 mice with lowered levels of DNA methylation, 23 developed tumors. None of the control group of 18 normal mice developed tumors in the same time period.
 (a)Explain why we cannot safely use either the large-sample confidence interval or the test for comparing the proportions of normal and altered mice that develop tumors.
 (b) The plus four method adds two observations, a success and a failure, to each sample. What are the sample sizes and the numbers of mice with tumors after? Give a plus four 99% confidence interval for the difference in the proportions of the two populations that develop tumors. 
 (c)Based on your confidence interval, is the difference between normal and altered mice significant at the 1% level?