COMSAE Phase 2 BSA 116/117/118/119
Practice-Based Learning & Improvement
Exam Questions &, Exams 2026 | 2027
UPDATED QUESTIONS WITH 100%
CORRECT ANSWERS, EXAMS
A 58-year-old man with hypertension is enrolled in a study evaluating
whether a new antihypertensive medication reduces stroke risk.
Participants are randomly assigned to receive either the new
medication or an identical placebo. Investigators and participants are
unaware of treatment assignment. Which feature of this study most
directly reduces confounding?
A) Blinding
B) Randomization
C) Placebo administration
D) Large sample size
✓✓ Correct Answer: B) Randomization
Rationale:
Randomization distributes known and unknown confounding variables
between treatment groups, making the groups more comparable at
baseline. Blinding primarily reduces information and performance bias,
while a placebo helps maintain blinding and controls for nonspecific
treatment effects. A large sample improves precision and statistical
power but does not inherently eliminate confounding. Randomized
Page 1 of 133
,controlled trials therefore provide strong evidence for causal treatment
effects when appropriately designed and conducted.
A researcher wants to determine whether long-term exposure to
occupational asbestos is associated with development of
mesothelioma. A group of workers exposed to asbestos and a
comparable group without occupational exposure are followed for 25
years. The incidence of mesothelioma is compared between groups.
Which study design is being used?
A) Case-control study
B) Cross-sectional study
C) Prospective cohort study
D) Ecologic study
✓✓ Correct Answer: C) Prospective cohort study
Rationale:
A prospective cohort study begins with participants classified according
to exposure status and follows them forward in time to determine
development of an outcome. This design allows direct calculation of
incidence and relative risk. A case-control study instead begins with
individuals who already have the outcome and looks backward for
exposure history. Cross-sectional studies assess exposure and outcome
at one point in time and generally cannot establish temporal sequence.
A study investigates whether prior exposure to a medication is
associated with a rare cancer. Investigators identify 300 patients with
the cancer and 600 controls without the cancer, then determine
whether each participant previously used the medication. Which
measure of association is most appropriate?
A) Relative risk
Page 2 of 133
,B) Odds ratio
C) Risk difference
D) Incidence rate
✓✓ Correct Answer: B) Odds ratio
Rationale:
Case-control studies begin with disease status and retrospectively
determine exposure. Because incidence and risk cannot be directly
calculated from a traditional case-control design, the odds ratio is the
appropriate measure of association. For rare diseases, the odds ratio
can approximate the relative risk when the controls accurately
represent the population from which the cases arose.
A clinical researcher wants to compare the prevalence of chronic kidney
disease among adults with and without diabetes using information
collected during a single community health survey. Which study design
is most appropriate?
A) Cross-sectional study
B) Prospective cohort study
C) Randomized controlled trial
D) Case-control study
✓✓ Correct Answer: A) Cross-sectional study
Rationale:
Cross-sectional studies measure exposure and outcome at a particular
point in time. They are useful for estimating prevalence and identifying
associations that may warrant further investigation. However, because
exposure and outcome are assessed simultaneously, temporal
Page 3 of 133
, relationships may be unclear. This limitation makes cross-sectional
studies less useful for establishing causality.
Investigators conduct a randomized trial of a new therapy for heart
failure. The treatment group has fewer hospitalizations than the control
group, but investigators conclude that the treatment caused the
reduction despite substantial differences in adherence between groups.
Which issue most threatens the validity of this conclusion?
A) Confounding
B) External validity
C) Publication bias
D) Recall bias
✓✓ Correct Answer: A) Confounding
Rationale:
A confounder is associated with both the exposure and outcome and
can distort the apparent relationship between them. If adherence
differs substantially between groups and adherence independently
affects hospitalization risk, adherence may confound the treatment-
outcome relationship. Publication bias concerns selective publication of
studies, recall bias involves inaccurate recollection of prior exposures,
and external validity concerns generalizability.
A systematic review identifies 12 randomized trials evaluating a
medication. The pooled results show substantial statistical
heterogeneity. Which finding most directly indicates heterogeneity?
A) I² = 78%
B) p = 0.04 for the pooled effect
C) Relative risk = 0.82
Page 4 of 133
Practice-Based Learning & Improvement
Exam Questions &, Exams 2026 | 2027
UPDATED QUESTIONS WITH 100%
CORRECT ANSWERS, EXAMS
A 58-year-old man with hypertension is enrolled in a study evaluating
whether a new antihypertensive medication reduces stroke risk.
Participants are randomly assigned to receive either the new
medication or an identical placebo. Investigators and participants are
unaware of treatment assignment. Which feature of this study most
directly reduces confounding?
A) Blinding
B) Randomization
C) Placebo administration
D) Large sample size
✓✓ Correct Answer: B) Randomization
Rationale:
Randomization distributes known and unknown confounding variables
between treatment groups, making the groups more comparable at
baseline. Blinding primarily reduces information and performance bias,
while a placebo helps maintain blinding and controls for nonspecific
treatment effects. A large sample improves precision and statistical
power but does not inherently eliminate confounding. Randomized
Page 1 of 133
,controlled trials therefore provide strong evidence for causal treatment
effects when appropriately designed and conducted.
A researcher wants to determine whether long-term exposure to
occupational asbestos is associated with development of
mesothelioma. A group of workers exposed to asbestos and a
comparable group without occupational exposure are followed for 25
years. The incidence of mesothelioma is compared between groups.
Which study design is being used?
A) Case-control study
B) Cross-sectional study
C) Prospective cohort study
D) Ecologic study
✓✓ Correct Answer: C) Prospective cohort study
Rationale:
A prospective cohort study begins with participants classified according
to exposure status and follows them forward in time to determine
development of an outcome. This design allows direct calculation of
incidence and relative risk. A case-control study instead begins with
individuals who already have the outcome and looks backward for
exposure history. Cross-sectional studies assess exposure and outcome
at one point in time and generally cannot establish temporal sequence.
A study investigates whether prior exposure to a medication is
associated with a rare cancer. Investigators identify 300 patients with
the cancer and 600 controls without the cancer, then determine
whether each participant previously used the medication. Which
measure of association is most appropriate?
A) Relative risk
Page 2 of 133
,B) Odds ratio
C) Risk difference
D) Incidence rate
✓✓ Correct Answer: B) Odds ratio
Rationale:
Case-control studies begin with disease status and retrospectively
determine exposure. Because incidence and risk cannot be directly
calculated from a traditional case-control design, the odds ratio is the
appropriate measure of association. For rare diseases, the odds ratio
can approximate the relative risk when the controls accurately
represent the population from which the cases arose.
A clinical researcher wants to compare the prevalence of chronic kidney
disease among adults with and without diabetes using information
collected during a single community health survey. Which study design
is most appropriate?
A) Cross-sectional study
B) Prospective cohort study
C) Randomized controlled trial
D) Case-control study
✓✓ Correct Answer: A) Cross-sectional study
Rationale:
Cross-sectional studies measure exposure and outcome at a particular
point in time. They are useful for estimating prevalence and identifying
associations that may warrant further investigation. However, because
exposure and outcome are assessed simultaneously, temporal
Page 3 of 133
, relationships may be unclear. This limitation makes cross-sectional
studies less useful for establishing causality.
Investigators conduct a randomized trial of a new therapy for heart
failure. The treatment group has fewer hospitalizations than the control
group, but investigators conclude that the treatment caused the
reduction despite substantial differences in adherence between groups.
Which issue most threatens the validity of this conclusion?
A) Confounding
B) External validity
C) Publication bias
D) Recall bias
✓✓ Correct Answer: A) Confounding
Rationale:
A confounder is associated with both the exposure and outcome and
can distort the apparent relationship between them. If adherence
differs substantially between groups and adherence independently
affects hospitalization risk, adherence may confound the treatment-
outcome relationship. Publication bias concerns selective publication of
studies, recall bias involves inaccurate recollection of prior exposures,
and external validity concerns generalizability.
A systematic review identifies 12 randomized trials evaluating a
medication. The pooled results show substantial statistical
heterogeneity. Which finding most directly indicates heterogeneity?
A) I² = 78%
B) p = 0.04 for the pooled effect
C) Relative risk = 0.82
Page 4 of 133
