PH 661 Biostatistics II – Spring 2021
Midterm
Instructor: Charles Edeki
Student Name: Date:
Solve the problem (4 points each)
18.
A researcher is interested in the toxicity of cigarette smoking in humans. One variable measure
that he decides to investigate involves measuring the pH of the urine from smokers to see if there
is an increase in toxicity. In to carry out a statistical test, the researcher collects a SRS of
61 current smokers from a population with a known standard deviation of 0.8.
A) If the researcher wants to be 95% confident about his estimate, calculate the margin of error
based on the above information.
B) Carry out the same calculation above, but assuming the researcher wishes to be “virtually
certain” about his estimate. (Use Z=3.0)
C) Compare the margin of errors calculated above.
21.
An investigator wants to determine if a new program aimed at reducing the overall number of
pregnancies in a highly populated area is effective (reducing average births below 6 per
household). In to carry out the investigation, the investigator conducts a SRS of 189
participants in the program and finds the average number of births is 4.7 with a sample standard
deviation of 0.9 births. Construct a 95% confidence interval for the average number of births per
household in this study. Provide a correct interpretation of your interval.
22.
Suppose a researcher is interested in the effectiveness of a new drug that is intended to naturally
increase hours of sleep for elderly patients experiencing insomnia. Suppose he collects
information from a group of 64 patients, and calculates a σ=.8 and a sample average of 6.4 hours
of sleep. Is there sufficient evidence to reject the null hypothesis that his treatment is ineffective
at increasing hours of sleep above 5 hours with 95% confidence?
23.
A research team wants to investigate the impact of increased sun exposure to a decrease in
depression. In to do so, the team gathers a SRS of 124 individuals with a sample average
score on the Geriatric Depression Scale (GDS) of 7.5 from a population with σ=.4 after
consistent sun exposure above 7 hours a day. Assume a clinical diagnosis for depression can only
be given with a GDS score of 9.
A) Is the team correct in their hypothesis?
B) State and interpret your results.
Multiple Choice (4 points each question)
24.
When the mean and median are equal, what can be said about the shape of the distribution?
A) More information should be presented if assumptions pertaining to the shape of the
distribution are to be made.
B) When the mean is equal to the median, the shape of the distribution tends to be slightly
skewed right.
C) When the mean is equal to the median, the shape of the distribution tends to be slightly
skewed left.
D) When the mean is equal to the median, the shape of the distribution can be assumed relatively
symmetrical.
25.
Removing a positive outlier from a dataset would do all but the following?
A) Reduce the average
B) Reduce the median
C) Increase the spread
D) Decrease the spread
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