Epidemiology — MCQs

Which of the following are the characteristic features of screening tests? 1. Done on healthy people 2. Done on unhealthy people 3. More accurate 4. Less accurate 5. Less expensive 6. More expensive 7. Not a basis for treatment 8. Used as a base for treatment Select the correct answer using the code given below:

Q1489

Analytical studies include the following methods of studies except:

Q1490

The denominator for calculating proportional mortality rate from a specific disease is:

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1481: The risk of disease is measured by

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

Explanation: ***Incidence Rate*** - **Incidence rate** measures the frequency of developing a new disease in a population over a specific period, thus directly reflecting the **risk** of disease occurrence. - It considers the number of **new cases** divided by the population at risk and provides insight into the dynamic process of becoming ill. *Prevalence Rate* - **Prevalence rate** measures the total number of existing cases of a disease in a population at a specific point in time or over a period. - It reflects the **burden** of disease but not the risk, as it includes both new and old cases. *Fatality Rate* - **Fatality rate** or **case fatality rate (CFR)** measures the proportion of individuals diagnosed with a disease who die from that disease. - It reflects the **severity** or prognosis of a disease, not the risk of acquiring it. *Attrition Rate* - **Attrition rate** refers to the rate of participants dropping out of a study or employees leaving an organization. - It is an indicator of **retention** or loss in a population, not the risk of disease.

Question 1482: Which of the following are the components of epidemiological triad?

A. Sensitivity, specificity and predictive value
B. Prevalence, incidence and attack rate
C. Time, place and person distribution
D. Agent, host and environmental factors (Correct Answer)

Explanation: ***Agent, host and environmental factors*** - The **epidemiological triad** is a traditional model that explains disease causation by focusing on the interaction between an infectious **agent**, a susceptible **host**, and the **environment** that brings them together. - Understanding these three components helps to analyze and prevent the spread of diseases. *Sensitivity, specificity and predictive value* - These terms relate to the **performance and accuracy of diagnostic tests**, assessing how well a test identifies true positives and true negatives. - They are measures used in the evaluation of screening programs and diagnostic procedures, not directly in the causation model. *Prevalence, incidence and attack rate* - These are **measures of disease occurrence** or frequency within a population, used to quantify the burden of disease. - While essential for understanding disease patterns, they describe the *results* of the disease process rather than the *factors* causing it. *Time, place and person distribution* - These refer to the **descriptive epidemiology** aspects of disease, outlining **who** is affected, **where** they are, and **when** the disease occurs. - These elements characterize disease patterns but are not the fundamental components responsible for disease causation in the epidemiological triad model.

Question 1483: Which of the following statements is NOT correct regarding case fatality rate?

A. It is the ratio of deaths to cases expressed as percentage
B. Very useful indicator for both acute and chronic diseases
C. Variation can occur for the same disease because of changes in the agent factors
D. One of the measures related to virulence (Correct Answer)

Explanation: ***One of the measures related to virulence*** - This statement is **incorrect**. The **case fatality rate (CFR)** is a measure of the **severity of a disease** within a specific population of affected individuals, typically related to a specific outbreak or period. - While it reflects disease severity, it is not a direct measure of **virulence**, which describes the pathogen's ability to cause damage to the host and is an intrinsic property of the infectious agent itself. *It is the ratio of deaths to cases expressed as percentage* - This is a **correct definition** of the case fatality rate (CFR), calculated as the number of deaths from a disease divided by the total number of cases of that disease, expressed as a percentage. - It quantifies the proportion of individuals diagnosed with a specific disease who ultimately die from it. *Very useful indicator for both acute and chronic diseases* - This statement is **correct**. The case fatality rate is a valuable indicator for assessing the severity and impact of both **acute diseases** (e.g., infectious outbreaks) and **chronic diseases** (e.g., cancer survival). - It helps in understanding the prognosis and lethality of a condition in affected individuals. *Variation can occur for the same disease because of changes in the agent factors* - This statement is **correct**. Case fatality rates for the same disease can vary significantly due to changes in **agent factors** (e.g., strain virulence, drug resistance), host factors (e.g., age, immune status), and environmental factors (e.g., access to healthcare). - For example, different strains of influenza can have varying case fatality rates due to differences in their inherent pathogenicity.

Question 1484: An important measure of communicability of a disease is

A. Secondary attack rate (Correct Answer)
B. Incidence rate
C. Prevalence rate
D. Case fatality rate

Explanation: ***Secondary attack rate*** - The **secondary attack rate** quantifies the probability of infection among **susceptible contacts** of a primary case. - It is a direct measure of the **person-to-person transmissibility** or **communicability** of an infectious disease within a defined population. - Calculated as: (Number of cases among contacts / Total number of susceptible contacts) × 100 *Incidence rate* - The **incidence rate** measures the rate at which **new cases** of a disease occur in a population over a specified period. - While related to disease spread, it does not specifically describe transmission from an existing case to a close contact. *Prevalence rate* - The **prevalence rate** measures the **proportion of individuals** in a population who have a disease at a specific point in time or over a period. - It reflects the burden of existing disease but provides no direct information about how easily the disease spreads from one person to another. *Case fatality rate* - The **case fatality rate** (CFR) indicates the **proportion of individuals** diagnosed with a disease who die from that disease. - It is a measure of the **severity or lethality** of a disease, not its communicability or transmissibility.

Question 1485: Denominator in calculation of case fatality rate is:

A. Total number of cases due to the disease concerned (Correct Answer)
B. Total number of hospital admissions
C. Total number of deaths due to all causes
D. Total number of deaths due to the disease concerned

Explanation: ***Total number of cases due to the disease concerned*** - The **case fatality rate (CFR)** measures the **proportion of deaths** among individuals diagnosed with a specific disease. - The denominator for CFR is defined as the **total number of confirmed cases** of that disease in a given population and time period. - Formula: CFR = (Deaths from disease / Total cases of disease) × 100 *Total number of hospital admissions* - This value represents the total number of individuals admitted to the hospital, which may include patients with various conditions, not just the specific disease of interest. - Using this as the denominator would incorrectly dilute the severity of the disease in question by including individuals not directly affected by it. *Total number of deaths due to all causes* - This figure encompasses all deaths in a population, regardless of cause, and is typically used in calculations like the **crude death rate**. - It does not specifically relate to the severity or outcome of a particular disease and therefore cannot serve as the denominator for case fatality. *Total number of deaths due to the disease concerned* - This value represents the **numerator** in the calculation of the case fatality rate, as it quantifies the number of deaths attributable to the specific disease. - Using it as the denominator would lead to a calculation of 100% if the number of deaths equals the number of cases, which would be incorrect for CFR calculations.

Question 1486: Which one of the following is FALSE regarding confounding factor in epidemiological studies ?

A. Source of bias is interpretation
B. Associated both with exposure and disease
C. Independent risk factor for disease in question
D. Distributed equally between study and control groups (Correct Answer)

Explanation: ***Distributed equally between study and control groups*** - A **confounding factor** is, by definition, **not equally distributed** between study (exposed) and control (unexposed) groups, as this unequal distribution leads to the observed bias. - If a potential confounder were equally distributed, it would not distort the relationship between the exposure and the outcome. *Source of bias is interpretation* - Confounding is a source of **bias in interpretation** because it can create a spurious association or mask a true one between an exposure and an outcome. - It leads to an incorrect conclusion about the causal relationship, even if the data collection itself was accurate. *Associated both with exposure and disease* - For a variable to be a confounder, it must be **associated with the exposure** being studied (e.g., smoking is associated with alcohol consumption). - It must also be an **independent risk factor for the disease** outcome (e.g., alcohol consumption is an independent risk factor for esophageal cancer). *Independent risk factor for disease in question* - A confounder must be an **independent risk factor** for the disease outcome, separate from its association with the primary exposure. - This means it influences the disease risk regardless of the exposure being investigated.

Question 1487: In a case control study, confounding factors can be minimized by the following EXCEPT:

A. Matching of variables such as age and sex
B. Stratification during analysis
C. Increasing sample size for cases and controls (Correct Answer)
D. Randomization during selection

Explanation: ***Increasing sample size for cases and controls*** - While increasing sample size improves the **precision** of an estimate and the statistical power of a study, it does **not** address or minimize **confounding factors**. - Confounding occurs when an extraneous variable distorts the observed association between an exposure and an outcome; a larger sample size might make the confounded association appear more statistically significant, but it **cannot remove the confounding itself**. - This is the method that does NOT minimize confounding. *Matching of variables such as age and sex* - **Matching** involves selecting controls that are similar to cases with respect to known confounding variables (e.g., age, sex, socioeconomic status). - This technique helps ensure that the groups being compared are balanced on these potential confounders, thereby **minimizing their influence** on the observed association. - Commonly used in case-control studies. *Stratification during analysis* - **Stratification** involves analyzing the association between exposure and outcome separately within subgroups (strata) defined by different levels of the confounding variable. - This allows researchers to assess if the association holds true within each stratum and estimate the true association **adjusted for the confounder**. - A standard analytical technique to control confounding. *Randomization during selection* - While **randomization** is primarily used in **randomized controlled trials (RCTs)** to distribute confounding factors equally between groups, **random selection of controls** in case-control studies can help ensure representativeness and minimize selection bias. - Although not the primary method for controlling confounding in case-control studies (where matching and stratification are preferred), random selection can contribute to reducing systematic differences between cases and controls. - This differs from "increasing sample size," which fundamentally cannot address confounding.

Question 1488: Which of the following are the characteristic features of screening tests? 1. Done on healthy people 2. Done on unhealthy people 3. More accurate 4. Less accurate 5. Less expensive 6. More expensive 7. Not a basis for treatment 8. Used as a base for treatment Select the correct answer using the code given below:

A. 1, 3, 5 and 8
B. 1, 4, 5 and 7 (Correct Answer)
C. 2, 3, 6 and 7
D. 2, 4, 5 and 8

Explanation: ***1, 4, 5 and 7*** - **Screening tests are applied to apparently healthy populations** to detect disease in the pre-symptomatic phase, enabling early intervention - They are **less accurate** (lower sensitivity/specificity) than diagnostic tests but designed for mass application - They must be **less expensive** to be feasible for large-scale population screening - Screening results are **not a basis for treatment** - positive screens require confirmatory diagnostic testing before treatment decisions *Incorrect: 1, 3, 5 and 8* - Screening tests are **less accurate**, not more accurate - they prioritize feasibility and cost-effectiveness over precision - Screening identifies candidates for further evaluation, **not a basis for immediate treatment** *Incorrect: 2, 3, 6 and 7* - Screening is done on **healthy (asymptomatic) people**, not unhealthy people - symptomatic individuals require diagnostic testing - Screening tests are **less expensive**, not more expensive, to enable population-wide application - Screening tests are **less accurate**, not more accurate than diagnostic tests *Incorrect: 2, 4, 5 and 8* - Screening is performed on **apparently healthy individuals**, not unhealthy people - Positive screening results require **diagnostic confirmation** before treatment - screening alone is not a basis for treatment

Question 1489: Analytical studies include the following methods of studies except:

A. Randomised controlled trials
B. Cohort studies
C. Case control studies
D. Cross sectional studies (Correct Answer)

Explanation: ***Cross sectional studies*** - **Cross-sectional studies** are generally classified as **descriptive studies** as they assess the prevalence of a disease and/or risk factors at a single point in time, rather than analyzing cause-and-effect relationships. - While they can identify associations, they cannot establish **temporality** or causality between an exposure and an outcome, which is a hallmark of analytical studies. *Randomised controlled trials* - **Randomized controlled trials (RCTs)** are the gold standard for analytical studies, specifically for evaluating interventions, due to their ability to establish **causality** through random assignment and control groups. - They are prospective in nature and aim to assess the effect of an intervention on an outcome, controlling for confounding. *Cohort studies* - **Cohort studies** are a type of **observational analytical study** where a group of individuals exposed to a risk factor and a group not exposed are followed over time to compare disease incidence. - They are crucial for studying rare exposures and the natural history of diseases, allowing for the calculation of incidence rates and relative risks. *Case control studies* - **Case-control studies** are **retrospective analytical studies** that compare individuals with a disease (cases) to individuals without the disease (controls) and look back in time to identify past exposures. - These studies are efficient for investigating rare diseases and multiple exposures for a single outcome, allowing for the calculation of odds ratios.

Question 1490: The denominator for calculating proportional mortality rate from a specific disease is:

A. Total deaths in that year (Correct Answer)
B. Attributable deaths of a particular disease
C. Mid-year population during that year
D. Population at risk in that particular area

Explanation: **_Total deaths in that year_** - The **proportional mortality rate** for a specific disease is calculated as the number of deaths from that disease divided by the **total deaths from all causes** in the same period. - This denominator provides the proportion of all deaths attributable to the specific disease, indicating its relative importance among all causes of death. *Attributable deaths of a particular disease* - This refers to the **numerator** of the proportional mortality rate for the specific disease, not the denominator. - It represents the outcome being measured as a proportion of all deaths. *Mid-year population during that year* - The **mid-year population** is the denominator for calculating **crude death rates** or **disease-specific mortality rates**, not proportional mortality rates. - It measures the risk of death in a given population over a period, rather than the proportion of deaths due to a specific cause. *Population at risk in that particular area* - The **population at risk** is typically used in the denominator for calculating **incidence rates** or **attack rates**. - This measures the likelihood of developing a disease or condition, not the proportion of deaths from a specific cause among all deaths.

Practice by Chapter

Principles of Epidemiology

Practice Questions

Measures of Disease Frequency

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Epidemiological Study Designs

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Descriptive Epidemiology

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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

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Association and Causation

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Modern Epidemiological Methods

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Critical Appraisal of Epidemiological Studies

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