Clinical Trials:
Public Health 7420
Sample Examination Questions
Note:
The final examination will primarily be based on material covered after the mid
term examination.
Since the material in the 2
nd
half of the course builds on material in
the 1
st
half, it is also a good idea to review notes from the 1st half of the course.
1. Give an example of a crossover study.
How does it differ from a parallel group
study?
2. Cite 2 advantages and 2 disadvantages of a crossover study design.
3. In the 2 period crossover design, why is a washout used between treatment
periods?
4. An investigator is planning to study the effects of a new treatment compared to
placebo on blood pressure lowering over a 4 week followup period.
Will sample
size be greater with a crossover study or a parallel group study?
Why?
5. Why does the test for interaction in the crossover study have low power?
6. Give 2 advantages and 2 disadvantages of narrow (restricted) versus broad (loose)
eligibility criteria.
7. Why are logs of patients considered for enrollment in a trial (i.e., log giving reasons
patients were not included in the trial) advocated by some investigators?
8. Why are runin periods used in trials?
Give 3 examples of different uses of runin
periods.
9.
If patients with elevated risk levels are to be randomized in a clinical trial, discuss
the factors which would influence the amount of regression toward the mean that
would be expected.
How can regression toward the mean be reduced?
10.
Men and women with cholesterol levels >
280 mg/dl are selected for a clinical trial of
a new cholesterol lowering drug with placebo. This cutpoint corresponds to the
upper 5% of the population to be screened.
Assume the correlation of two
cholesterol readings on a subject is 0.70.
What is the expected regression toward
the mean if the standard deviation of cholesterol measurements is 40 mg/dl?
11. If the cutpoint used for eligibility was changed to 250 mg/dl, what impact would this
have on the expected amount of regression to the mean assuming the same
population is to be screened?
1
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View Full Document12. A trial is planned to study the effect of drug treatment on CVD morbidity and
mortality among participants with systolic BP 130139 mmHg.
One site plans to
screen from the general population (e.g., shopping centers) and one site (an
HMO) plans to screen all participants who had an elevated BP at their last
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 Spring '07
 ph7420
 Clinical trial, Crossover study, Halperin

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