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EXAMS
ANSWERS | Questions & Answers (Verified Answers) With Rationales
( Update)
This Document Contains:
110 Questions with Correct, Detailed and Verified Answers
2026/2027 Actual Exam Testbank
Questions & Answers (Verified Answers) With Rationales
100% Guaranteed Pass
Complete A+ Guide
Page 1
,Question 1
In a randomized controlled trial investigating a novel kinase inhibitor for metastatic melanoma,
the primary endpoint is progression-free survival (PFS). The study uses a 2:1 randomization ratio
favoring the experimental arm. Which statistical consideration is most critical to ensure the
validity of the log-rank test used for comparing PFS between groups?
A) The assumption of proportional hazards must hold over the entire follow-up period.
B) The sample size must be adjusted for the 2:1 allocation to maintain 80% power.
C) Crossover from placebo to experimental arm must be accounted for via intention-to-treat analysis.
D) Stratification by BRAF mutation status is required to reduce confounding.
Answer: A) The assumption of proportional hazards must hold over the entire follow-up period.
Explanation: The log-rank test is most powerful under proportional hazards; violation can lead to
loss of power and misinterpretation. While sample size adjustment (B) is important for
power, it does not directly affect test validity. Crossover (C) and stratification (D)
address other biases but not the core assumption of the test.
Question 2
A researcher plans a case-control study to examine the association between a novel genetic variant
and a rare autoimmune disease. The variant has a population prevalence of 5%. Which design
feature is most critical to minimize bias from population stratification?
A) Matching cases and controls on age and sex.
B) Selecting controls from the same geographic region as cases.
C) Using genomic control methods or principal component analysis.
D) Ensuring equal numbers of cases and controls.
Answer: C) Using genomic control methods or principal component analysis.
Explanation: Population stratification arises from systematic ancestry differences; genomic control or
PCA adjusts for ancestry, reducing false positives. Matching on age/sex (A) or
geography (B) may not fully capture genetic ancestry. Equal numbers (D) affect power,
not bias.
Page 2
,Question 3
In a cohort study of occupational exposure to benzene, the outcome is leukemia incidence. The
exposure is measured as cumulative ppm-years. Which approach best handles the time-varying
nature of exposure to estimate the exposure-response relationship?
A) Cox proportional hazards model with cumulative exposure as a time-dependent covariate.
B) Logistic regression with exposure categorized into quartiles.
C) Poisson regression with person-years and average exposure.
D) Linear regression of log-transformed leukemia rates on exposure.
Answer: A) Cox proportional hazards model with cumulative exposure as a time-dependent
covariate.
Explanation: Cox model with time-dependent covariates properly accounts for changing exposure
over time and censoring. Logistic regression (B) ignores time and censoring. Poisson
regression (C) can handle person-time but typically uses fixed exposure. Linear
regression (D) is inappropriate for rates and censored data.
Question 4
A diagnostic test for a disease has a sensitivity of 95% and specificity of 90%. The prevalence of
the disease in the screened population is 1%. What is the positive predictive value (PPV) of the
test?
A) 8.8%
B) 9.6%
C) 50.0%
D) 86.4%
Answer: A) 8.8%
Explanation: PPV = (sensitivity × prevalence) / (sensitivity × prevalence + (1-specificity) ×
(1-prevalence)) = (0.95×0.01) / (0.95×0.01 + 0.10×0.99) = 0.0095 / (0.0095+0.099) "H
0.0876 = 8.76%. Option A (8.8%) is closest. Option B (9.6%) is common if
miscomputing. Options C and D are gross overestimates.
Page 3
, Question 5
In a meta-analysis of 12 randomized trials comparing drug A to placebo for hypertension, the
pooled effect estimate shows a mean reduction in systolic blood pressure of 5 mmHg (95% CI: 2 to
8 mmHg). The I² statistic is 65%. Which interpretation is most appropriate?
A) The result is clinically insignificant because the effect size is small.
B) There is moderate to substantial heterogeneity that may affect the generalizability of the pooled
estimate.
C) The confidence interval is wide, indicating imprecise estimate, so the result is not statistically
significant.
D) The fixed-effects model should be used because heterogeneity is present.
Answer: B) There is moderate to substantial heterogeneity that may affect the generalizability of the
pooled estimate.
Explanation: An I² of 65% indicates substantial heterogeneity, suggesting variability across studies;
a random-effects model is typically preferred. The effect is statistically significant (CI
does not include 0) and may be clinically relevant (5 mmHg). Fixed-effects model (D) is
inappropriate with high heterogeneity.
Question 6
A phase II trial of a new chemotherapy agent uses a Simon's two-stage minimax design. In the first
stage, 15 patients are enrolled; if 2 or fewer respond, the trial stops. If 3 or more respond, an
additional 25 patients are enrolled. The null hypothesis is that the response rate is "d10%, and the
alternative is that it is "e30%. With ±=0.05 and ²=0.20, what is the probability of early termination
if the true response rate is 10%?
A) 0.184
B) 0.816
C) 0.950
D) 0.999
Answer: B) 0.816
Explanation: Under null (p=0.10), probability of "d2 responses in 15 is binomial: P(X"d2) =
sum_{k=0}^2 C(15,k) (0.10)^k (0.90)^(15-k) "H 0.8159. Thus early termination
probability is 0.816. Option A is the complement (0.184). Options C and D are
incorrect.
Page 4
Download Download
EXAMS
ANSWERS | Questions & Answers (Verified Answers) With Rationales
( Update)
This Document Contains:
110 Questions with Correct, Detailed and Verified Answers
2026/2027 Actual Exam Testbank
Questions & Answers (Verified Answers) With Rationales
100% Guaranteed Pass
Complete A+ Guide
Page 1
,Question 1
In a randomized controlled trial investigating a novel kinase inhibitor for metastatic melanoma,
the primary endpoint is progression-free survival (PFS). The study uses a 2:1 randomization ratio
favoring the experimental arm. Which statistical consideration is most critical to ensure the
validity of the log-rank test used for comparing PFS between groups?
A) The assumption of proportional hazards must hold over the entire follow-up period.
B) The sample size must be adjusted for the 2:1 allocation to maintain 80% power.
C) Crossover from placebo to experimental arm must be accounted for via intention-to-treat analysis.
D) Stratification by BRAF mutation status is required to reduce confounding.
Answer: A) The assumption of proportional hazards must hold over the entire follow-up period.
Explanation: The log-rank test is most powerful under proportional hazards; violation can lead to
loss of power and misinterpretation. While sample size adjustment (B) is important for
power, it does not directly affect test validity. Crossover (C) and stratification (D)
address other biases but not the core assumption of the test.
Question 2
A researcher plans a case-control study to examine the association between a novel genetic variant
and a rare autoimmune disease. The variant has a population prevalence of 5%. Which design
feature is most critical to minimize bias from population stratification?
A) Matching cases and controls on age and sex.
B) Selecting controls from the same geographic region as cases.
C) Using genomic control methods or principal component analysis.
D) Ensuring equal numbers of cases and controls.
Answer: C) Using genomic control methods or principal component analysis.
Explanation: Population stratification arises from systematic ancestry differences; genomic control or
PCA adjusts for ancestry, reducing false positives. Matching on age/sex (A) or
geography (B) may not fully capture genetic ancestry. Equal numbers (D) affect power,
not bias.
Page 2
,Question 3
In a cohort study of occupational exposure to benzene, the outcome is leukemia incidence. The
exposure is measured as cumulative ppm-years. Which approach best handles the time-varying
nature of exposure to estimate the exposure-response relationship?
A) Cox proportional hazards model with cumulative exposure as a time-dependent covariate.
B) Logistic regression with exposure categorized into quartiles.
C) Poisson regression with person-years and average exposure.
D) Linear regression of log-transformed leukemia rates on exposure.
Answer: A) Cox proportional hazards model with cumulative exposure as a time-dependent
covariate.
Explanation: Cox model with time-dependent covariates properly accounts for changing exposure
over time and censoring. Logistic regression (B) ignores time and censoring. Poisson
regression (C) can handle person-time but typically uses fixed exposure. Linear
regression (D) is inappropriate for rates and censored data.
Question 4
A diagnostic test for a disease has a sensitivity of 95% and specificity of 90%. The prevalence of
the disease in the screened population is 1%. What is the positive predictive value (PPV) of the
test?
A) 8.8%
B) 9.6%
C) 50.0%
D) 86.4%
Answer: A) 8.8%
Explanation: PPV = (sensitivity × prevalence) / (sensitivity × prevalence + (1-specificity) ×
(1-prevalence)) = (0.95×0.01) / (0.95×0.01 + 0.10×0.99) = 0.0095 / (0.0095+0.099) "H
0.0876 = 8.76%. Option A (8.8%) is closest. Option B (9.6%) is common if
miscomputing. Options C and D are gross overestimates.
Page 3
, Question 5
In a meta-analysis of 12 randomized trials comparing drug A to placebo for hypertension, the
pooled effect estimate shows a mean reduction in systolic blood pressure of 5 mmHg (95% CI: 2 to
8 mmHg). The I² statistic is 65%. Which interpretation is most appropriate?
A) The result is clinically insignificant because the effect size is small.
B) There is moderate to substantial heterogeneity that may affect the generalizability of the pooled
estimate.
C) The confidence interval is wide, indicating imprecise estimate, so the result is not statistically
significant.
D) The fixed-effects model should be used because heterogeneity is present.
Answer: B) There is moderate to substantial heterogeneity that may affect the generalizability of the
pooled estimate.
Explanation: An I² of 65% indicates substantial heterogeneity, suggesting variability across studies;
a random-effects model is typically preferred. The effect is statistically significant (CI
does not include 0) and may be clinically relevant (5 mmHg). Fixed-effects model (D) is
inappropriate with high heterogeneity.
Question 6
A phase II trial of a new chemotherapy agent uses a Simon's two-stage minimax design. In the first
stage, 15 patients are enrolled; if 2 or fewer respond, the trial stops. If 3 or more respond, an
additional 25 patients are enrolled. The null hypothesis is that the response rate is "d10%, and the
alternative is that it is "e30%. With ±=0.05 and ²=0.20, what is the probability of early termination
if the true response rate is 10%?
A) 0.184
B) 0.816
C) 0.950
D) 0.999
Answer: B) 0.816
Explanation: Under null (p=0.10), probability of "d2 responses in 15 is binomial: P(X"d2) =
sum_{k=0}^2 C(15,k) (0.10)^k (0.90)^(15-k) "H 0.8159. Thus early termination
probability is 0.816. Option A is the complement (0.184). Options C and D are
incorrect.
Page 4
