Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1471: The ratio between incidences among exposed and non-exposed persons is called

A. Positive predictive value
B. Relative risk (Correct Answer)
C. Attributable risk
D. Odds ratio

Explanation: ***Correct: Relative risk*** - This is the ratio of the **incidence of disease** in an **exposed group** to the incidence of disease in an **unexposed group**. - It quantifies the likelihood of developing the disease in the exposed group relative to the unexposed group. - **Formula:** RR = (Incidence in exposed) / (Incidence in unexposed) *Incorrect: Positive predictive value* - This statistical measure indicates the probability that a person with a **positive test result** actually has the disease. - It is not a measure of incidence comparison between exposed and unexposed populations. *Incorrect: Attributable risk* - This measures the **absolute difference** in incidence rates between exposed and unexposed groups. - It quantifies the amount of disease incidence that can be directly attributed to the exposure, not a ratio. - **Formula:** AR = (Incidence in exposed) - (Incidence in unexposed) *Incorrect: Odds ratio* - This is a measure of association between an **exposure and an outcome**, representing the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. - It is commonly used in **case-control studies** and is a ratio of odds, not directly incidence rates.

Question 1472: Which of the following constitutes "Secondary Prevention"?

A. Health Education Programme
B. Using Limb Callipers
C. Wearing Safety Helmets
D. Screening Tests (Correct Answer)

Explanation: ***Screening Tests (Correct)*** - **Screening tests** constitute the core of **secondary prevention**, designed to detect disease in its **early, asymptomatic stages** before clinical symptoms appear. - By identifying disease early, screening enables **prompt intervention** to prevent progression, reduce morbidity, and improve prognosis. - Examples include mammography for breast cancer, PAP smear for cervical cancer, and blood pressure screening for hypertension. *Health Education Programme* - Health education programmes are examples of **primary prevention**, which aims to **prevent disease occurrence** by promoting healthy behaviors and reducing risk factors. - These interventions target healthy individuals to maintain health and prevent disease onset, not to detect existing disease. *Using Limb Callipers* - **Limb callipers** are used for anthropometric measurements or as assistive devices for mobility in patients with disabilities. - As a measurement tool, it's used for **assessment and monitoring**, not for disease prevention. - As an assistive device, it falls under **tertiary prevention** (rehabilitation), helping patients manage existing disability. *Wearing Safety Helmets* - Wearing safety helmets is a classic example of **primary prevention**, as it aims to **prevent injuries** (head trauma) from occurring in the first place. - It is a protective measure implemented before any health event occurs, not for early disease detection.

Question 1473: The "Relative Risk" of 0.25 indicates

A. 2.5 times higher risk in the exposed individuals compared with the unexposed
B. 25% increase in the incidence rate in the exposed individuals compared with the unexposed
C. 75% reduction in the incidence rate in the exposed individuals compared with the unexposed (Correct Answer)
D. 75% risk increase in the exposed individuals compared with the unexposed

Explanation: ***75% reduction in the incidence rate in the exposed individuals compared with the unexposed*** - A **Relative Risk (RR)** of 0.25 means the risk in the exposed group is 25% of the risk in the unexposed group. - This indicates a **reduction** in risk calculated as (1 - RR) * 100%, so (1 - 0.25) * 100% = 75% reduction. *2.5 times higher risk in the exposed individuals compared with the unexposed* - This would be indicated by an RR of 2.5, meaning the risk is **2.5 times greater** in the exposed group. - An RR of 0.25 signifies a risk that is **less than** that of the unexposed group, not higher. *25% increase in the incidence rate in the exposed individuals compared with the unexposed* - A 25% increase would mean the RR is 1.25 (1 + 0.25), indicating a **higher risk** in the exposed group. - An RR of 0.25 represents a **decrease** in risk, not an increase. *75% risk increase in the exposed individuals compared with the unexposed* - A 75% risk increase would correspond to an RR of 1.75 (1 + 0.75), suggesting a **greater risk**. - With an RR of 0.25, the risk in the exposed group is **lower**, representing a reduction rather than an increase.

Question 1474: The "risk of a disease" is measured by the

A. Prevalence Rate
B. Incidence Rate (Correct Answer)
C. Case Fatality Rate
D. Communicability Rate

Explanation: ***Incidence Rate*** - The **incidence rate** directly measures the frequency of **new cases** of a disease in a population over a specified period. - It is used to estimate the **risk** or probability of developing a disease, as it quantifies how quickly people are contracting the disease within the at-risk population. - **Formula:** (Number of new cases during time period / Population at risk) × multiplier - This is the epidemiologically correct measure of disease risk. *Prevalence Rate* - The **prevalence rate** measures the **total number of existing cases** (both new and old) of a disease in a population at a specific point in time or over a period. - It reflects the **burden** of a disease, not the risk of acquiring it, as it includes individuals who may have developed the disease much earlier. - Prevalence = Incidence × Duration of disease. *Case Fatality Rate* - The **case fatality rate** (CFR) measures the **proportion of individuals diagnosed with a disease who die from that disease** within a specified period. - It reflects the **severity** or lethality of a disease among those affected, not the risk of developing the disease in the first place. - CFR is a measure of disease outcome, not disease occurrence. *Communicability Rate* - There is no standard epidemiological term exactly defined as "communicability rate"; however, related concepts include the **basic reproduction number (R₀)** and **secondary attack rate**. - These concepts describe the **spread or transmissibility of an infectious disease**, not the risk of contracting a disease from a general population perspective. - This measures transmission dynamics rather than individual risk.

Question 1475: Consider the following demographic parameters : 1. Average number of daughters born to a woman 2. Sum of age-specific fertility rates 3. Magnitude of completed family size Which of the above parameters reflect/reflects total fertility rate?

A. 1 only
B. 2 and 3 (Correct Answer)
C. 1 and 3
D. 3 only

Explanation: ***2 and 3*** - The **total fertility rate (TFR)** is precisely defined as the **sum of age-specific fertility rates (ASFR)** across all reproductive age groups (15-49 years), representing the average number of children a woman would bear if she experienced current age-specific fertility rates throughout her reproductive life. - TFR conceptually indicates the **magnitude of completed family size** under current fertility conditions, though technically TFR is a period (synthetic cohort) measure while completed family size is an observed cohort measure. - Parameter 2 is the **direct definition**, while parameter 3 represents the **conceptual interpretation** of what TFR indicates. *1 only* - The "average number of daughters born to a woman" represents the **Gross Reproduction Rate (GRR)**, not TFR. - GRR = TFR × proportion of female births (approximately 0.49). - **TFR includes all live births** regardless of sex, making this parameter incorrect for TFR. *1 and 3* - Parameter 1 represents GRR, not TFR, making this combination incorrect. - Including an incorrect parameter invalidates this option despite parameter 3 having conceptual relevance. *3 only* - While completed family size has conceptual relationship to TFR, this option omits parameter 2, which is the **primary and precise definition** of TFR. - TFR is calculated as the sum of ASFRs, not measured from actual completed families, making this incomplete.

Question 1476: A study done in UK of 5174 births at home and 11156 births in hospitals showed perinatal mortality rates of 5.4/1000 in home births and 27.8/1000 in hospital births. What kind of Association is this?

A. Spurious Association (Correct Answer)
B. Indirect Association
C. Temporal Association
D. Direct Association

Explanation: ***Spurious Association*** - A **spurious association** occurs when two variables appear to be causally related but are not, often due to a confounding variable. - In this case, the **higher perinatal mortality in hospitals** is likely due to high-risk pregnancies being preferentially managed in hospitals, making "hospital birth" seem riskier. *Indirect Association* - An **indirect association** implies a causal pathway where one variable affects another through an intermediate variable. - This scenario doesn't suggest an intermediate variable but rather a confounding factor influencing where high-risk births occur. *Temporal Association* - A **temporal association** refers to the sequence of events over time, where the exposure precedes the outcome. - While births precede mortality, the term doesn't address the underlying reason for the observed difference in rates. *Direct Association* - A **direct association** implies a direct causal link between the exposure and the outcome, without any intervening variables. - Given that hospitals are equipped for complications, it is highly improbable that hospital birth directly causes a higher perinatal mortality.

Question 1477: In a cohort study spanning 20 years, 50 out of 5000 smokers developed lung cancer, and 10 out of 10000 non-smokers developed lung cancer. What is the 'relative risk' among smokers for developing lung cancer?

A. 10 (Correct Answer)
B. 5
C. 45
D. 50

Explanation: ***Correct Answer: 10*** - The incidence of lung cancer in smokers = 50/5000 = 0.01 (1%) - The incidence of lung cancer in non-smokers = 10/10000 = 0.001 (0.1%) - **Relative Risk (RR) = Incidence in exposed / Incidence in unexposed** - RR = 0.01 / 0.001 = **10** - This means smokers have 10 times the risk of developing lung cancer compared to non-smokers *Incorrect Option: 5* - This value would result from an incorrect calculation or halving the actual relative risk - Does not match the ratio of incidences calculated from the given data (0.01/0.001 ≠ 5) - Would underestimate the true risk among smokers *Incorrect Option: 45* - This does not represent any standard epidemiological measure from this data - May result from confusion with absolute numbers or incorrect arithmetic - Neither the absolute risk difference nor any valid ratio yields this number *Incorrect Option: 50* - This represents the **absolute number of cases** in the smoking cohort, not a risk measure - Relative risk is a **ratio** comparing incidence rates between groups, not a count - Common error: confusing absolute numbers with relative measures

Question 1478: Why is matching done in a case-control study?

A. To remove the effect of unknown confounders
B. To remove the effect of known confounders (Correct Answer)
C. To eliminate selection bias
D. To eliminate interviewer’s bias

Explanation: ***To remove the effect of known confounders*** - **Matching** in a case-control study helps to control for the influence of specific variables (known confounders) that might otherwise distort the observed association between the exposure and outcome. - By matching cases and controls on characteristics like age, sex, or socioeconomic status, researchers ensure that these factors are similarly distributed in both groups, isolating the effect of the primary exposure. *To remove the effect of unknown confounders* - Matching is effective for **known confounders** that are identified and controlled during study design. - It does not address the impact of **unknown** or unmeasured confounding variables, which can still influence the study's results. *To eliminate selection bias* - **Selection bias** occurs when participants are not representative of the target population; matching primarily addresses confounding, not the initial selection process. - While careful selection is crucial to minimize selection bias, matching itself is more related to controlling for nuisance variables *after* selection. *To eliminate interviewer’s bias* - **Interviewer bias** (or observer bias) arises when the interviewer's expectations or knowledge influence data collection or interpretation. - This type of bias is typically addressed through blinding (e.g., blinded interviewers, participants, or outcome assessors), not through matching study participants.

Question 1479: Which of the following items are among the uses of epidemiology?

A. To study historically the rise and fall of the diseases
B. All of these (Correct Answer)
C. To identify syndromes
D. To arrive at community diagnosis

Explanation: ***All of these*** - Epidemiology encompasses various applications, and all three listed items are well-established uses of this discipline in public health practice. - Each of the following represents a distinct but complementary application of epidemiological principles. **To study historically the rise and fall of diseases:** - This is a fundamental application of epidemiology, as **epidemiological studies** track disease prevalence and incidence over time to understand their natural history and the impact of interventions. - Historical data helps in predicting future trends, understanding the **etiology** of diseases, and evaluating the effectiveness of public health measures. - This temporal perspective is essential for identifying emerging and re-emerging diseases. **To identify syndromes:** - Epidemiology plays a crucial role in defining and characterizing **syndromes** by observing patterns of symptoms, signs, and associated factors within a population. - This involves statistical analysis to link sets of clinical features to a common underlying condition or exposure. - Classic examples include identifying AIDS as a syndrome and recognizing new clinical entities through pattern recognition. **To arrive at community diagnosis:** - **Community diagnosis** involves assessing the health status of a community, identifying health problems, and determining their causes and risk factors using epidemiological methods. - This process is essential for planning and implementing effective public health interventions and allocating resources appropriately. - It forms the foundation for evidence-based public health planning and policy development.

Question 1480: Retrospective cohort studies have the following features EXCEPT:

A. Investigator goes back in time to select study groups
B. Generally more expensive than prospective studies (Correct Answer)
C. Outcomes have occurred before the start of the study
D. Results are obtained more quickly

Explanation: ***Generally more expensive than prospective studies*** - Retrospective cohort studies are typically **less expensive** than prospective studies because they utilize existing data, thus avoiding the costs associated with new data collection and long-term follow-up. - The primary expenses in retrospective studies often involve data retrieval and analysis, which are generally lower compared to the extensive resources needed for prospective data acquisition. *Investigator goes back in time to select study groups* - This is a hallmark feature of **retrospective cohort studies**, where researchers define study groups (exposed and unexposed) based on past exposures. - Data collection then proceeds by looking forward from the exposure to identify health outcomes that have already occurred. *Outcomes have occurred before the start of the study* - In a **retrospective cohort study**, both the exposure and the **outcomes of interest** have already taken place before the study officially begins. - Researchers identify existing records to link past exposures to these pre-existing outcomes. *Results are obtained more quickly* - Because all exposures and outcomes have already occurred and data is often readily available, **retrospective studies** can generate results much faster than prospective studies. - They do not require waiting for events to unfold in real-time, which significantly reduces the duration of the research process.

Practice by Chapter

Principles of Epidemiology

Practice Questions

Measures of Disease Frequency

Practice Questions

Epidemiological Study Designs

Practice Questions

Descriptive Epidemiology

Practice Questions

Analytical Epidemiology

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Experimental Epidemiology

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Screening for Disease

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Surveillance Systems

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Investigation of an Epidemic

Practice Questions

Association and Causation

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Modern Epidemiological Methods

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Critical Appraisal of Epidemiological Studies

Practice Questions

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