Posted: September 16th, 2017

Math 104 Lab Assignment #4 – Lab Assignment #4: Review of Two ­Sample Test 2014..

Math 104 ­ Fall ‘14
Applied Regression Analysis

Lab Assignment #4: Review of Two­Sample Test

Department of Mathematics

GOLDEN GATE UNIVERSITY

Math 104 Fall ’14

Lab Assignment #4

[1] Lipitor is a drug used to control cholesterol. In clinical trials of Lipitor, 94 subjects were treated with
Lipitor and 270 subjects were given a placebo. Among those who were treated with Lipitor, 7 developed
infections. Among those given a placebo, 27 developed infections. Use a 0.05 significance level to test the
claim that the rate of infections was the same for those treated with Lipitor and those given a placebo.

Math 104 Fall ’14

Lab Assignment #4

[2] Simple random samples of high­interest (5.36%) mortgages and low­interest (3.77%) mortgage were
obtained. For the 40 high­interest mortgages, the borrowers had a mean FICO credit score of 594.8 and
standard deviation of 12.2. For the 40 low­interest mortgages, the borrowers had a mean FICO credit score
of 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 high­
interest mortgage is lower than the mean FICO score of borrowers with low­interest mortgage.

b) Does the FICO credit rating score appear to affect mortgage payments? If so, how?

Math 104 Fall ’14

Lab Assignment #4

[3] A random sample of the birth weights of 186 babies has a mean of 3103g and a standard deviation of
696g (based on data from “Cognitive Outcomes of Preschool Children with Prenatal Cocaine Exposure,” by
Singer et al., Journal of the American Medical Association, Vol. 291, No. 20). These babies were born to
mothers who did not use cocaine during their pregnancies. Further, a random sample of the birth weights
of 190 babies born to mothers who used cocaine during their pregnancies has a mean of 2700g and a
standard deviation of 645g.

a) The birth weights of babies are known normally distributed. Use a 0.05 significance level to test the
claim 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 between
the mean birth weight of a baby born to mothers who did not use cocaine and that of a baby born to
mothers 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 ’14

Lab Assignment #4

[4] A large discount chain compares the performance if its credit managers in Ohio and Illinois by
comparing the mean dollars amounts owed by customers with delinquent charge accounts in these two
states. Here a small mean dollar amount owed is desirable because it indicates that bad credit risks are not
being extended large amounts of credit. Two independent, random samples of delinquent accounts are
selected 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 $524
with a standard deviation of $38. The second sample, which consists of 20 randomly selected delinquent
accounts 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 equal
with ? =0.05.

b) Test with ? =0.05 whether there is a difference between the population mean dollar amounts owed
by 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 95
percent confidence interval for the difference between the mean dollar amounts owed in Ohio and
Illinois. Based on this interval, do you think that these mean dollar amounts differ in a practically

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