1. Which feature primarily distinguishes an analytical study from a descriptive study?
A. Randomization
B. Presence of a comparison group
C. Large sample size
D. Long follow-up
Answer: B
2. In analytical observational studies, the investigator:
A. Assigns the exposure randomly
B. Manipulates the intervention
C. Does not assign exposure but compares exposure patterns between groups
D. Selects only diseased individuals
Answer: C
3. Analytical observational studies are mainly designed to:
A. Estimate disease prevalence
B. Generate hypotheses only
C. Evaluate associations between exposure and disease
D. Measure mortality
Answer: C
4. Which of the following is NOT an analytical study?
A. Cohort study
B. Case-control study
C. Cross-sectional analytical study
D. Case report
Answer: D
5. Which analytical study progresses from exposure to outcome?
A. Case-control study
B. Cohort study
C. Ecological study
D. Case series
Answer: B
6. Which analytical study progresses from outcome to previous exposure?
A. Cohort study
B. Cross-sectional study
C. Case-control study
D. Clinical trial
Answer: C
7. Which analytical study measures exposure and disease simultaneously?
A. Prospective cohort
B. Case-control
C. Cross-sectional analytical study
D. Retrospective cohort
Answer: C
8. The direction of inquiry in a cohort study is:
A. Disease → Exposure
B. Exposure → Disease
C. Disease → Treatment
D. Exposure → Recovery
Answer: B
9. The principal purpose of an analytical study is to:
A. Describe disease distribution
B. Test an association between exposure and outcome
C. Measure prevalence only
D. Report unusual clinical findings
Answer: B
10. Which measure of association is commonly calculated in a cohort study?
A. Odds Ratio
B. Relative Risk
C. Hazard Ratio only
D. Prevalence Ratio
Answer: B
11. Which measure of association is commonly calculated in a case-control study?
A. Relative Risk
B. Risk Difference
C. Odds Ratio
D. Incidence Rate
Answer: C
12. The term cohort originally comes from:
A. Greek medicine
B. Roman military
C. Egyptian civilization
D. Medieval hospitals
Answer: B
13. In epidemiology, a cohort refers to:
A. Patients admitted to one hospital
B. Individuals sharing a common characteristic
C. Individuals with the same disease
D. Laboratory workers
Answer: B
14. Which of the following is an example of a cohort?
A. All patients with diabetes admitted today
B. All babies born in 2026
C. Patients attending one OPD
D. Lung cancer cases
Answer: B
15. In a cohort study investigating smoking and lung cancer, smokers represent the:
A. Outcome group
B. Control group
C. Exposed cohort
D. Case group
Answer: C
16. Individuals without the exposure under investigation are called:
A. Cases
B. Controls
C. Unexposed cohort
D. Outcomes
Answer: C
17. In a cohort study, participants should be free from the disease at:
A. End of follow-up
B. Baseline
C. Time of analysis only
D. Any stage
Answer: B
18. Which quantity is directly compared between exposed and unexposed groups in a cohort study?
A. Prevalence
B. Mortality only
C. Incidence
D. Odds
Answer: C
19. Which statement regarding cohort studies is CORRECT?
A. Participants are selected based on disease status.
B. Participants are selected based on exposure status.
C. Exposure is assigned by investigators.
D. Cases and controls are selected.
Answer: B
20. A researcher follows smokers and non-smokers for ten years to compare lung cancer incidence. This is:
A. Case-control study
B. Ecological study
C. Cohort study
D. Cross-sectional study
Answer: C
21. Which type of cohort study begins before both exposure and disease have occurred?
A. Retrospective cohort
B. Prospective cohort
C. Ambispective cohort
D. Historical cohort
Answer: B
22. In a retrospective cohort study:
A. Exposure and outcome occur after study initiation.
B. Both exposure and disease have already occurred when the study begins.
C. Participants are randomized.
D. Disease is measured before exposure.
Answer: B
23. An ambispective cohort study combines:
A. Descriptive and analytical studies
B. Prospective and retrospective approaches
C. Cohort and case-control studies
D. Cross-sectional and ecological studies
Answer: B
24. Which famous cohort study identified major cardiovascular risk factors?
A. Doll and Hill Study
B. Nurses’ Health Study
C. Framingham Heart Study
D. Whitehall Study
Answer: C
25. Which statement BEST summarizes cohort studies?
A. Participants are selected based on disease status and previous exposure is assessed.
B. Participants are selected according to exposure status, followed over time, and disease incidence is compared to estimate Relative Risk.
C. Exposure and disease are measured simultaneously.
D. They estimate only disease prevalence.
Answer: B
26. Which is the FIRST step in conducting a cohort study?
A. Analysis of data
B. Selection of exposed and unexposed individuals
C. Follow-up
D. Measurement of outcome
Answer: B
27. Which of the following is NOT one of the major elements of a cohort study?
A. Selection of study population
B. Gathering baseline information
C. Random allocation of exposure
D. Follow-up and analysis
Answer: C
28. The primary objective of collecting baseline information in a cohort study is to:
A. Diagnose disease
B. Assess exposure status accurately
C. Calculate Relative Risk immediately
D. Measure mortality
Answer: B
29. During baseline assessment in a cohort study, individuals already having the disease are usually excluded because they:
A. Increase study cost
B. Are no longer at risk of developing the disease
C. Reduce sample size
D. Cannot be followed
Answer: B
30. Which type of information is commonly collected during baseline assessment?
A. Exposure status
B. Identification details
C. Other risk factors (co-variables)
D. All of the above
Answer: D
31. A cohort selected from the general population is exemplified by:
A. Cancer registry
B. Framingham Heart Study
C. Doll and Hill Study
D. Hospital registry
Answer: B
32. Which is an example of a special exposure cohort?
A. Birth cohort
B. Occupational workers exposed to asbestos
C. School children
D. General population sample
Answer: B
33. Which comparison group consists of unexposed individuals from the same study population?
A. External comparison group
B. Historical control
C. Internal comparison group
D. Matched control
Answer: C
34. An external comparison group is mainly used when:
A. Randomization is possible
B. Internal unexposed individuals are unavailable
C. Disease prevalence is high
D. Sample size is small
Answer: B
35. In the study of workers exposed to aniline dyes, the comparison group was obtained from:
A. Smokers
B. Hospital controls
C. General population statistics
D. Family members
Answer: C
36. Which principle is essential for maintaining validity during follow-up in a cohort study?
A. Differential surveillance
B. Uniform surveillance in exposed and unexposed groups
C. Different diagnostic criteria
D. Selective follow-up
Answer: B
37. Standardized diagnosis of outcomes is important because cohort studies often:
A. Include only healthy participants
B. Continue for long periods
C. Use only retrospective data
D. Measure prevalence
Answer: B
38. Which of the following introduces bias in a cohort study?
A. Equal follow-up
B. Differential loss to follow-up
C. Standardized outcome assessment
D. Internal comparison group
Answer: B
39. In the standard 2 × 2 table of a cohort study, a represents:
A. Exposed individuals who develop disease
B. Exposed individuals without disease
C. Unexposed individuals with disease
D. Unexposed individuals without disease
Answer: A
40. The incidence among exposed individuals is calculated as:
A. a/(a+c)
B. a/(a+b)
C. a/(b+d)
D. a/(c+d)
Answer: B
41. The incidence among unexposed individuals is:
A. c/(c+d)
B. c/(a+c)
C. d/(c+d)
D. b/(a+b)
Answer: A
42. Relative Risk (RR) is calculated as:
A. Odds in exposed ÷ Odds in unexposed
B. Incidence in exposed ÷ Incidence in unexposed
C. Prevalence in exposed ÷ Prevalence in unexposed
D. Disease odds ÷ Exposure odds
Answer: B
43. If RR = 1, the interpretation is:
A. Exposure increases disease risk.
B. Exposure decreases disease risk.
C. No association exists between exposure and disease.
D. Disease always follows exposure.
Answer: C
44. If RR > 1, the exposure is interpreted as:
A. Protective
B. Harmful or positively associated with disease
C. Unrelated to disease
D. Impossible to interpret
Answer: B
45. If RR < 1, the exposure is most likely:
A. A risk factor
B. Positively associated
C. Protective against disease
D. A confounder
Answer: C
46. A study reports RR = 3.5 for smoking and lung cancer. This means:
A. Smokers have 3.5 times the incidence of lung cancer compared with non-smokers.
B. Lung cancer causes smoking.
C. Smoking prevalence is 3.5%.
D. Three and a half smokers develop lung cancer.
Answer: A
47. Which feature is a major strength of cohort studies?
A. They are ideal for rare diseases.
B. They directly measure incidence.
C. They do not require follow-up.
D. They calculate only prevalence.
Answer: B
48. Cohort studies are particularly useful for studying:
A. Rare diseases
B. Rare exposures
C. Short-term outcomes only
D. Hospital outbreaks only
Answer: B
49. Which characteristic provides strong evidence for causal inference in cohort studies?
A. Simultaneous measurement of exposure and disease
B. Clear temporal relationship between exposure and outcome
C. Selection based on disease
D. Absence of comparison groups
Answer: B
50. Which statement BEST summarizes cohort studies?
A. Participants are selected according to disease status, and past exposure is compared.
B. Participants are selected according to exposure status, followed over time, incidence is calculated, and Relative Risk is used to measure association.
C. Exposure and disease are measured simultaneously.
D. Only prevalence can be estimated.
Answer: B
51. Which of the following is NOT a strength of a cohort study?
A. Ability to calculate incidence
B. Ability to study multiple outcomes of a single exposure
C. Suitable for rare diseases
D. Clear temporal relationship between exposure and disease
Answer: C
52. Cohort studies are generally not recommended for rare diseases because:
A. Exposure cannot be measured.
B. Very large sample sizes and prolonged follow-up are required.
C. Relative Risk cannot be calculated.
D. Cases cannot be identified.
Answer: B
53. Which disease is LEAST suitable for investigation using a prospective cohort study?
A. Hypertension
B. Lung cancer
C. Creutzfeldt–Jakob disease (rare disease)
D. Coronary artery disease
Answer: C
54. A major limitation of prospective cohort studies is:
A. Inability to calculate incidence
B. Absence of comparison groups
C. Long duration and high cost
D. Inability to assess temporality
Answer: C
55. Which type of bias is introduced when participants in the exposed group are more likely to be lost during follow-up than those in the unexposed group?
A. Recall bias
B. Detection bias
C. Attrition (Loss-to-follow-up) bias
D. Observer bias
Answer: C
56. A researcher follows 2,000 smokers and 2,000 non-smokers for 15 years to evaluate lung cancer incidence. Which epidemiological measure can be calculated directly?
A. Odds Ratio
B. Relative Risk
C. Prevalence Ratio
D. Case Fatality Rate
Answer: B
57. Which of the following characteristics makes a cohort study particularly valuable for causal inference?
A. Selection based on disease status
B. Exposure is measured before disease develops
C. Cases and controls are selected first
D. Disease prevalence is measured
Answer: B
58. A cohort study begins with disease-free individuals. Why is this important?
A. To calculate prevalence
B. To ensure only incident cases occur during follow-up
C. To reduce sample size
D. To eliminate confounding
Answer: B
59. Which statement regarding temporality is TRUE?
A. Disease occurs before exposure.
B. Exposure occurs before disease, strengthening causal inference.
C. Exposure and disease occur simultaneously.
D. Temporality cannot be assessed in cohort studies.
Answer: B
60. A Relative Risk (RR) of 0.40 indicates that:
A. Exposure increases disease risk by 40%.
B. Exposure reduces disease occurrence and may be protective.
C. Exposure has no association with disease.
D. Disease risk is four times higher.
Answer: B
61. Which of the following cohort studies would most likely require an external comparison group?
A. General population cohort
B. Birth cohort
C. Occupational cohort where every participant is exposed
D. Framingham Heart Study
Answer: C
62. Which statement regarding internal comparison groups is CORRECT?
A. They are selected from another country.
B. They consist of unexposed individuals within the same study population.
C. They are selected after outcome occurrence.
D. They are always hospital patients.
Answer: B
63. Which of the following best illustrates a prospective cohort study?
A. Reviewing hospital records from 1990–2010
B. Identifying smokers today and following them until 2040
C. Interviewing lung cancer patients about smoking history
D. Conducting a prevalence survey
Answer: B
64. Which example best illustrates a retrospective cohort study?
A. Following healthy individuals for twenty years
B. Using employment records and mortality records to evaluate disease occurrence
C. Selecting cancer patients and controls
D. Measuring hypertension prevalence
Answer: B
65. An ambispective cohort study combines:
A. Descriptive and analytical studies
B. Prospective and retrospective follow-up
C. Cross-sectional and cohort methods
D. Case-control and experimental methods
Answer: B
66. Which of the following is a classic example of a retrospective cohort study discussed in the lecture?
A. Framingham Heart Study
B. Doll and Hill Study
C. Aniline dye workers and bladder cancer study
D. Nurses’ Health Study
Answer: C
67. In the Framingham Heart Study, hypertension was considered the:
A. Outcome
B. Exposure (risk factor)
C. Confounder
D. Control variable
Answer: B
68. Which of the following is an important objective of collecting baseline information?
A. To estimate disease prevalence
B. To define individuals at risk and measure exposure before disease develops
C. To calculate odds ratio
D. To identify prevalent cases for analysis
Answer: B
69. Which characteristic of cohort studies makes them useful for studying multiple outcomes?
A. Participants are selected based on disease.
B. Participants are classified according to exposure.
C. Outcomes are measured simultaneously.
D. Controls are matched.
Answer: B
70. Which statement regarding rare exposures is TRUE?
A. Case-control studies are always preferred.
B. Cohort studies are particularly efficient because exposed individuals can be identified first.
C. Rare exposures cannot be studied.
D. Relative Risk cannot be estimated.
Answer: B
71. A study reports:
- Incidence among smokers = 18%
- Incidence among non-smokers = 6%
What is the Relative Risk (RR)?
A. 0.33
B. 2
C. 3
D. 6
Answer: C
Explanation: RR = 18/6 = 3
72. A Relative Risk of 1.0 indicates:
A. Smoking is protective.
B. Exposure triples disease risk.
C. No association exists between exposure and disease.
D. Disease cannot occur.
Answer: C
73. Which statement best distinguishes a cohort study from a case-control study?
A. Cohort studies begin with exposure, whereas case-control studies begin with disease.
B. Both begin with disease.
C. Both begin with exposure.
D. Cohort studies cannot estimate incidence.
Answer: A
74. Which feature contributes MOST to the internal validity of a cohort study?
A. Equal and complete follow-up of exposed and unexposed participants
B. Large sample size only
C. Selecting hospital patients only
D. Using prevalent cases
Answer: A
75. Which statement BEST summarizes the strengths and weaknesses of cohort studies?
A. Cohort studies directly calculate incidence and establish temporal relationships but require large samples, long follow-up, and are inefficient for rare diseases.
B. Cohort studies are inexpensive and ideal for rare diseases.
C. Cohort studies cannot calculate Relative Risk.
D. Cohort studies measure only prevalence.
Answer: A
76. A researcher identifies 5,000 factory workers exposed to asbestos in 2026 and follows them for 20 years to determine the incidence of lung cancer. Which study design is being used?
A. Case-control study
B. Cross-sectional study
C. Prospective cohort study
D. Ecological study
Answer: C
77. Investigators use employment records from 1980–2000 and cancer registry data from 2000–2025 to study asbestos exposure and mesothelioma. Which study design is this?
A. Cross-sectional study
B. Retrospective cohort study
C. Case-control study
D. Randomized controlled trial
Answer: B
78. Which analytical study is most appropriate for investigating a rare disease?
A. Prospective cohort study
B. Retrospective cohort study
C. Case-control study
D. Cross-sectional study
Answer: C
79. Which analytical study is most efficient for studying a rare exposure?
A. Case-control study
B. Cohort study
C. Cross-sectional study
D. Ecological study
Answer: B
80. A cohort study demonstrates a Relative Risk (RR) of 5.2 between smoking and lung cancer. Which interpretation is MOST appropriate?
A. Smoking is unrelated to lung cancer.
B. Smokers have approximately five times the risk of developing lung cancer compared with non-smokers.
C. Lung cancer increases smoking by five times.
D. Five smokers will develop lung cancer.
Answer: B
81. Which scenario best illustrates temporality, one of Bradford Hill’s important considerations for causation?
A. Exposure measured after disease diagnosis.
B. Exposure measured before disease occurrence.
C. Exposure and disease measured simultaneously.
D. Disease measured before exposure.
Answer: B
82. A study follows participants for 25 years. At the end, 35% of exposed participants are lost to follow-up compared with only 5% of unexposed participants. Which bias is MOST likely?
A. Recall bias
B. Attrition (loss-to-follow-up) bias
C. Interviewer bias
D. Publication bias
Answer: B
83. Which strategy BEST minimizes bias during follow-up in a cohort study?
A. More frequent follow-up only in exposed participants
B. Uniform surveillance and identical outcome assessment in both groups
C. Excluding participants with mild disease
D. Recruiting hospital patients only
Answer: B
84. Which statement regarding Relative Risk (RR) is TRUE?
A. RR can only be calculated in case-control studies.
B. RR compares disease incidence between exposed and unexposed groups.
C. RR measures prevalence.
D. RR always equals Odds Ratio.
Answer: B
85. A cohort study reports:
- Incidence among exposed = 30%
- Incidence among unexposed = 10%
The Relative Risk equals:
A. 0.33
B. 2
C. 3
D. 10
Answer: C
86. A Relative Risk of 0.25 indicates that exposure:
A. Increases disease risk fourfold.
B. Has no association with disease.
C. Is associated with a 75% lower disease risk compared with the unexposed group.
D. Cannot be interpreted.
Answer: C
87. Which feature provides the strongest evidence supporting a causal relationship in cohort studies?
A. Simultaneous assessment of exposure and disease
B. Selection based on disease
C. Clear chronological sequence between exposure and outcome
D. Measurement of prevalence only
Answer: C
88. Which characteristic makes the Framingham Heart Study a landmark cohort study?
A. It was the first randomized clinical trial.
B. It identified major cardiovascular risk factors through long-term follow-up.
C. It measured disease prevalence only.
D. It investigated only hospital patients.
Answer: B
89. Which statement regarding case-control studies is CORRECT?
A. Participants are selected according to exposure.
B. Disease incidence is calculated directly.
C. Participants are selected according to disease status and previous exposure is assessed.
D. Relative Risk is calculated directly.
Answer: C
90. In a case-control study, the principal measure of association is:
A. Relative Risk
B. Incidence Density
C. Odds Ratio
D. Risk Difference
Answer: C
91. Which statement best explains why Odds Ratio rather than Relative Risk is calculated in case-control studies?
A. Disease incidence cannot be measured because sampling begins with cases and controls.
B. Exposure cannot be measured.
C. Cases are followed over time.
D. Participants are randomized.
Answer: A
92. Which type of case is generally preferred in case-control studies?
A. Prevalent case
B. Incident case
C. Historical case
D. Hospital survivor
Answer: B
93. Why are incident cases preferred over prevalent cases?
A. They are easier to identify.
B. They reduce survival (Neyman) bias.
C. They eliminate recall bias completely.
D. They increase prevalence.
Answer: B
94. Which source of cases is most representative of the source population?
A. Tertiary hospital
B. Referral center
C. Population-based disease registry
D. Specialty clinic
Answer: C
95. Controls in a case-control study should ideally:
A. Have the disease under investigation.
B. Represent the exposure distribution of the population that produced the cases.
C. Be selected according to exposure status.
D. Be relatives of cases only.
Answer: B
96. Which source of controls was used in the classic Doll and Hill study on smoking and lung cancer?
A. General population
B. Hospital patients with diseases other than lung cancer
C. Family members
D. Occupational workers
Answer: B
97. Which characteristic is ESSENTIAL for selecting controls?
A. Controls must have identical exposure as cases.
B. Controls should come from the same source population as the cases.
C. Controls must have the same disease.
D. Controls should all be healthy volunteers.
Answer: B
98. During a case-control study, investigators ask participants about smoking history over the previous 30 years. Which bias is particularly important?
A. Lead-time bias
B. Recall bias
C. Attrition bias
D. Performance bias
Answer: B
99. Which analytical study design would be MOST appropriate for rapidly investigating an outbreak of a very rare neurological disorder suspected to be associated with pesticide exposure?
A. Prospective cohort study
B. Cross-sectional survey
C. Case-control study
D. Ecological study
Answer: C
100. Which statement BEST summarizes the differences between cohort and case-control studies?
A. Cohort studies begin with exposure, calculate incidence and Relative Risk, establish temporality, and are efficient for rare exposures; case-control studies begin with disease, estimate Odds Ratio, are efficient for rare diseases, and cannot directly calculate incidence.
B. Both studies begin with disease and calculate Relative Risk.
C. Both studies begin with exposure and estimate Odds Ratio.
D. Cohort studies and case-control studies are identical except for sample size.
Answer: A
