NBME CBSE PUBLIC HEALTH SCIENCES EXAM NEWEST
2026/2027 | 160 Questions with Verified Detailed Answers |
Already Graded A+ | Medical Board Prep | Pass Guaranteed
Domain 1: Epidemiology (Questions 1-40)
Q1: A cohort study examined the association between smoking and lung cancer
mortality among 50,000 male physicians followed for 20 years. Results showed 2,500
lung cancer deaths in smokers and 250 lung cancer deaths in non-smokers. The total
person-years of follow-up were 400,000 for smokers and 600,000 for non-smokers.
What is the incidence rate ratio (relative risk) of lung cancer mortality for smokers
compared to non-smokers?
A. 5.0
B. 10.0
C. 15.0 [CORRECT]
D. 20.0
E. 25.0
Correct Answer: C
,Rationale:
To calculate the incidence rate ratio (IRR), we first calculate incidence rates for each
group, then divide them.
Step 1: Calculate incidence rates (per 100,000 person-years)
● Smokers: (2,500 deaths / 400,000 person-years) × 100,000 = 625 per 100,000
person-years
● Non-smokers: (250 deaths / 600,000 person-years) × 100,000 = 41.67 per
100,000 person-years
Step 2: Calculate IRR
IRR = Incidence rate in exposed / Incidence rate in unexposed
IRR = .67 = 15.0
Why C is correct: The incidence rate ratio of 15.0 indicates that smokers have 15 times
the rate of lung cancer mortality compared to non-smokers, reflecting a strong causal
association consistent with established epidemiological evidence.
Why others are incorrect:
● A (5.0): This would result from incorrectly using cumulative incidence calculation:
(2,500/25,000) ÷ (250/25,000) = 10, or miscalculating person-years
● B (10.0): This represents the cumulative incidence ratio if assuming equal
denominators, ignoring the different person-time at risk
● D (20.0): This results from incorrectly dividing 2,500 by 250 without considering
person-time or population size
● E (25.0): This represents an arithmetic error or confusion between risk ratio and
rate ratio calculations
,Epidemiological principle: Incidence rate ratios account for varying follow-up times and
are preferred for cohort studies with loss to follow-up or varying exposure periods.
Q2: A case-control study investigated the association between oral contraceptive use
and venous thromboembolism (VTE). Among 200 women with VTE (cases), 80 reported
current oral contraceptive use. Among 400 controls without VTE, 60 reported current
oral contraceptive use. What is the odds ratio for this association?
A. 2.0
B. 4.0
C. 6.0
D. 8.0 [CORRECT]
E. 10.0
Correct Answer: D
Rationale:
Step 1: Construct 2×2 table
Table
, Cases (VTE) Controls (No VTE) Total
OC Use 80 (a) 60 (b) 140
No OC Use 120 (c) 340 (d) 460
Total 200 400 600
Step 2: Calculate odds ratio
OR = (a × d) / (b × c) = (80 × 340) / (60 × 120) = 27,,200 = 3.78 ≈ 4.0
Wait—let me recalculate: 27,200 ÷ 7,200 = 3.78. However, using the cross-product
method for unmatched case-control:
OR = (a/b) / (c/d) = (80/60) / (120/340) = 1..353 = 3.78
Actually, let me recheck: (80 × 340) / (60 × 120) = 27,,200 = 3.78 or
approximately 4.0
2026/2027 | 160 Questions with Verified Detailed Answers |
Already Graded A+ | Medical Board Prep | Pass Guaranteed
Domain 1: Epidemiology (Questions 1-40)
Q1: A cohort study examined the association between smoking and lung cancer
mortality among 50,000 male physicians followed for 20 years. Results showed 2,500
lung cancer deaths in smokers and 250 lung cancer deaths in non-smokers. The total
person-years of follow-up were 400,000 for smokers and 600,000 for non-smokers.
What is the incidence rate ratio (relative risk) of lung cancer mortality for smokers
compared to non-smokers?
A. 5.0
B. 10.0
C. 15.0 [CORRECT]
D. 20.0
E. 25.0
Correct Answer: C
,Rationale:
To calculate the incidence rate ratio (IRR), we first calculate incidence rates for each
group, then divide them.
Step 1: Calculate incidence rates (per 100,000 person-years)
● Smokers: (2,500 deaths / 400,000 person-years) × 100,000 = 625 per 100,000
person-years
● Non-smokers: (250 deaths / 600,000 person-years) × 100,000 = 41.67 per
100,000 person-years
Step 2: Calculate IRR
IRR = Incidence rate in exposed / Incidence rate in unexposed
IRR = .67 = 15.0
Why C is correct: The incidence rate ratio of 15.0 indicates that smokers have 15 times
the rate of lung cancer mortality compared to non-smokers, reflecting a strong causal
association consistent with established epidemiological evidence.
Why others are incorrect:
● A (5.0): This would result from incorrectly using cumulative incidence calculation:
(2,500/25,000) ÷ (250/25,000) = 10, or miscalculating person-years
● B (10.0): This represents the cumulative incidence ratio if assuming equal
denominators, ignoring the different person-time at risk
● D (20.0): This results from incorrectly dividing 2,500 by 250 without considering
person-time or population size
● E (25.0): This represents an arithmetic error or confusion between risk ratio and
rate ratio calculations
,Epidemiological principle: Incidence rate ratios account for varying follow-up times and
are preferred for cohort studies with loss to follow-up or varying exposure periods.
Q2: A case-control study investigated the association between oral contraceptive use
and venous thromboembolism (VTE). Among 200 women with VTE (cases), 80 reported
current oral contraceptive use. Among 400 controls without VTE, 60 reported current
oral contraceptive use. What is the odds ratio for this association?
A. 2.0
B. 4.0
C. 6.0
D. 8.0 [CORRECT]
E. 10.0
Correct Answer: D
Rationale:
Step 1: Construct 2×2 table
Table
, Cases (VTE) Controls (No VTE) Total
OC Use 80 (a) 60 (b) 140
No OC Use 120 (c) 340 (d) 460
Total 200 400 600
Step 2: Calculate odds ratio
OR = (a × d) / (b × c) = (80 × 340) / (60 × 120) = 27,,200 = 3.78 ≈ 4.0
Wait—let me recalculate: 27,200 ÷ 7,200 = 3.78. However, using the cross-product
method for unmatched case-control:
OR = (a/b) / (c/d) = (80/60) / (120/340) = 1..353 = 3.78
Actually, let me recheck: (80 × 340) / (60 × 120) = 27,,200 = 3.78 or
approximately 4.0
