# Math 104 Lab Assignment #4 – Lab Assignment #4: Review of Two Â­Sample Test (Fall â14)

Math 104 Â­ Fall â14Applied Regression AnalysisLab Assignment #4: Review of TwoÂ­Sample TestDepartment of MathematicsGOLDEN GATE UNIVERSITYMath 104 Fall ’14Lab Assignment #4[1] Lipitor is a drug used to control cholesterol. In clinical trials of Lipitor, 94 subjects were treated withLipitor and 270 subjects were given a placebo. Among those who were treated with Lipitor, 7 developedinfections. Among those given a placebo, 27 developed infections. Use a 0.05 significance level to test theclaim that the rate of infections was the same for those treated with Lipitor and those given a placebo.Math 104 Fall ’14Lab Assignment #4[2] Simple random samples of highÂ­interest (5.36%) mortgages and lowÂ­interest (3.77%) mortgage wereobtained. For the 40 highÂ­interest mortgages, the borrowers had a mean FICO credit score of 594.8 andstandard deviation of 12.2. For the 40 lowÂ­interest mortgages, the borrowers had a mean FICO credit scoreof 785.2 and standard deviation of 16.3.a) Use a 0.01 significance level to test the claim that the mean FICO score of borrowers with highÂ­interest mortgage is lower than the mean FICO score of borrowers with lowÂ­interest mortgage.b) Does the FICO credit rating score appear to affect mortgage payments? If so, how?Math 104 Fall ’14Lab Assignment #4[3] A random sample of the birth weights of 186 babies has a mean of 3103g and a standard deviation of696g (based on data from âCognitive Outcomes of Preschool Children with Prenatal Cocaine Exposure,â bySinger et al., Journal of the American Medical Association, Vol. 291, No. 20). These babies were born tomothers who did not use cocaine during their pregnancies. Further, a random sample of the birth weightsof 190 babies born to mothers who used cocaine during their pregnancies has a mean of 2700g and astandard deviation of 645g.a) The birth weights of babies are known normally distributed. Use a 0.05 significance level to test theclaim that both samples are from populations having the same standard deviation.b) Using your finding in (a), construct a 95% confidence interval estimate of the difference betweenthe mean birth weight of a baby born to mothers who did not use cocaine and that of a baby born tomothers who used cocaine during their pregnancies.c) Using your finding in (b), does cocaine use appear to affect the birth weight of a baby? Substantiate you conclusion.Math 104 Fall ’14Lab Assignment #4[4] A large discount chain compares the performance if its credit managers in Ohio and Illinois bycomparing the mean dollars amounts owed by customers with delinquent charge accounts in these twostates. Here a small mean dollar amount owed is desirable because it indicates that bad credit risks are notbeing extended large amounts of credit. Two independent, random samples of delinquent accounts areselected from the populations of delinquent accounts in Ohio and Illinois, respectively. The first sample,which consists of 15 randomly selected delinquent accounts in Ohio, givens a mean dollar amount of \$524with a standard deviation of \$38. The second sample, which consists of 20 randomly selected delinquentaccounts in Illinois, gives a mean dollar amount of \$473 with a standard deviation of \$22.a) Assuming that the normality assumption, test to determine if the population variances are equalwith ? =0.05.b) Test with ? =0.05 whether there is a difference between the population mean dollar amounts owedby consumers with delinquent charge accounts in Ohio and Illinois.c) Assuming that the normality assumption and the condition you checked in a) hold, calculate a 95percent confidence interval for the difference between the mean dollar amounts owed in Ohio andIllinois. Based on this interval, do you think that these mean dollar amounts differ in a practicallyimportant way?
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