NR 503 EPIDEMIOLOGY FINAL EXAM (Latest)
Question
A randomized, double-blind clinical trial of a varicella vaccine observed an estimated incidence
of 25% chickenpox episodes in persons receiving the vaccine, compared to 80% among persons
receiving a placebo. The estimated efficacy of the vaccine is:
55.0%
65.0%
68.8%
71.4%
80.0%
Explanation
The efficacy is calculated by subtracting the rate in those vaccinated from the placebo rate and
dividing by the placebo rate. In this example, 80% minus 25% equals 55%. Dividing by 80%
results in an efficacy of 68.8%.
, Question
A study is conducted for a pharmaceutical agent that has shown promise for reducing heart
disease among women. In order to more fully test the agent, an additional study is done
restricting the participants to be randomized to those who have a history of hypertension. Which
of the following advantages cannot be claimed by the researchers?
Power of the study is increased
Potential benefits in high-risk populations are increased
Validity of the study is increased by focus on a homogenous population
The generalizability of the study is increased
The overall cost of the study is decreased
Explanation
Restricting the study to a high-risk group will only fail to increase the generalizability of the
findings since the study results will apply only to a more specific group of women who share a
history of hypertension.
Question
A new drug treatment for cardiac thrombus claims to have a higher success rate than the current
drug. A strong sign of the potential success is the lack of internal hemorrhaging starting 2 days
after treatment. 168 patients who require treatment for cardiac thrombi are randomized after
agreeing to participate in a trial of the new drug. The researchers were interested in whether the
Question
A randomized, double-blind clinical trial of a varicella vaccine observed an estimated incidence
of 25% chickenpox episodes in persons receiving the vaccine, compared to 80% among persons
receiving a placebo. The estimated efficacy of the vaccine is:
55.0%
65.0%
68.8%
71.4%
80.0%
Explanation
The efficacy is calculated by subtracting the rate in those vaccinated from the placebo rate and
dividing by the placebo rate. In this example, 80% minus 25% equals 55%. Dividing by 80%
results in an efficacy of 68.8%.
, Question
A study is conducted for a pharmaceutical agent that has shown promise for reducing heart
disease among women. In order to more fully test the agent, an additional study is done
restricting the participants to be randomized to those who have a history of hypertension. Which
of the following advantages cannot be claimed by the researchers?
Power of the study is increased
Potential benefits in high-risk populations are increased
Validity of the study is increased by focus on a homogenous population
The generalizability of the study is increased
The overall cost of the study is decreased
Explanation
Restricting the study to a high-risk group will only fail to increase the generalizability of the
findings since the study results will apply only to a more specific group of women who share a
history of hypertension.
Question
A new drug treatment for cardiac thrombus claims to have a higher success rate than the current
drug. A strong sign of the potential success is the lack of internal hemorrhaging starting 2 days
after treatment. 168 patients who require treatment for cardiac thrombi are randomized after
agreeing to participate in a trial of the new drug. The researchers were interested in whether the
