Homework 4 – Due November 10, 2015
Problem 1 (by hand)
In a length of hospitalization study conducted by several cooperating hospitals, a random sample of 24
peptic ulcer patients was drawn from a list of all peptic ulcer patients ever admitted to the participating
hospitals and the length of hospitalization per admission was determined for each. The mean length of
hospitalization per admission was found to be 8.15 with a standard deviation of 3 days. Assume that the
length of hospitalization of peptic ulcer patients is approximately normally distributed.
(a) Construct and interpret a 90% confidence interval for the true length of stay for peptic ulcer patients.
(b) Based on other studies we can say that the true length of stay for duodenal ulcer patients is 9 days.
Do we have sufficient evidence in the data to conclude that the length of stay for peptic ulcer
patients is significantly lower than duodenal ulcer patients? (Define the parameter(s), state the
hypotheses, fix alpha, compute the test statistic and the p-value, and state the decision and
conclusion in the context of the problem).
Problem 2 (using SAS; include SAS commands and SAS output)
Some studies of Alzheimer’s disease (AD) have shown an increase in CO2 production in patients with the
disease. In one such study the following CO2 values were obtained from 12 neocortical biopsy samples
from AD patients.
1008
1280
1181
1235
1548
2362
1956
1080
1458
2052
1756
1350
(a) Compute a 95% confidence interval for the true mean CO2 value in AD patients. Interpret it in the
context of the problem.
(b) Do we have sufficient evidence in the data to conclude that the true average CO2 value in AD
patients is different from 1100? (Define the parameter(s), state the hypotheses, fix alpha, give the
value of the test statistic and the p-value, and state your decision and conclusion in the context of the
problem).
(c) Do we have sufficient evidence in the data that the true average CO2 value in AD patients is below
2000? (Define the parameter(s), state the hypotheses, fix alpha, give the value of test statistic and the
p-value, and state your decision and conclusion in the context of the problem).
(d) Discuss if the parametric methods used in parts (a)-(c) are appropriate. Justify your answer.
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