Epidemiology Practice Questions

Q: The risk of disease is measured by

Incidence Rate. ***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.

Q: Which of the following are the components of epidemiological triad?

Agent, host and environmental factors. ***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.

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

One of the measures related to virulence. ***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.

Q: An important measure of communicability of a disease is

Secondary attack rate. ***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.

Q: Denominator in calculation of case fatality rate is:

Total number of cases due to the disease concerned. ***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.

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

Distributed equally between study and control groups. ***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.

Q: 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:

1, 4, 5 and 7. ***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

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

Total deaths in that year. **_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.

Q: Consider the following diseases: 1. Measles 2. Polio 3. Staphylococcal food poisoning 4. Typhoid Which of the above are the correct examples for incubation period of 10-14 days?

1 and 4. ***1 and 4*** - **Measles** has a typical incubation period of **10 to 14 days** from exposure to the onset of fever, fitting perfectly within the specified range. - **Typhoid fever** (caused by *Salmonella Typhi*) has an incubation period ranging from **7 to 21 days**, with **10-14 days being the average**, making it a correct example. *2 and 4* - **Polio** has an incubation period of **3 to 35 days** (commonly 6 to 20 days), which is too broad and variable to be classified specifically as a 10-14 day incubation disease. - Typhoid does fit the 10-14 day range, but Polio does not specifically match this criterion. *3 and 4* - **Staphylococcal food poisoning** has a very short incubation period of **30 minutes to 6 hours** due to preformed toxins, making it completely outside the 10-14 day range. - While Typhoid fits, Staphylococcal food poisoning clearly does not. *1 and 3* - While **Measles** correctly has a 10-14 day incubation period, **Staphylococcal food poisoning** has only **30 minutes to 6 hours**, making this combination incorrect.

Q: When the prevalence rate is used without any qualification, it is taken to mean as

point prevalence rate. ***point prevalence rate*** - When the term "prevalence rate" is used without any further specification, it is generally understood to refer to the **point prevalence rate**. - This measures the **proportion of individuals** in a population who have a disease or health condition at a **specific point in time**. *period prevalence rate* - The **period prevalence rate** refers to the proportion of individuals who have a disease or condition over a **specified period of time** (e.g., a year). - It is a cumulative measure over a duration, unlike the instantaneous 'point' measure. *mean duration prevalence rate* - There isn't a standard epidemiological measure specifically termed "mean duration prevalence rate." - Prevalence is related to duration, but this is a **statistical relationship** (Prevalence = Incidence x Duration), not a standard direct prevalence measure itself. *annual prevalence rate* - The **annual prevalence rate** is a type of **period prevalence rate** that specifically covers a one-year period. - While common, it is a specific qualification of prevalence, not the default meaning when "prevalence rate" is used generally.

Question 1

The risk of disease is measured by

Accepted Answer

Incidence Rate

Answer

Prevalence Rate

Answer

Fatality Rate

Answer

Attrition Rate

Question 2

Which of the following are the components of epidemiological triad?

Accepted Answer

Agent, host and environmental factors

Answer

Sensitivity, specificity and predictive value

Answer

Prevalence, incidence and attack rate

Answer

Time, place and person distribution

Question 3

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

Accepted Answer

One of the measures related to virulence

Answer

It is the ratio of deaths to cases expressed as percentage

Answer

Very useful indicator for both acute and chronic diseases

Answer

Variation can occur for the same disease because of changes in the agent factors

Question 4

An important measure of communicability of a disease is

Accepted Answer

Secondary attack rate

Answer

Incidence rate

Answer

Prevalence rate

Answer

Case fatality rate

Question 5

Denominator in calculation of case fatality rate is:

Accepted Answer

Total number of cases due to the disease concerned

Answer

Total number of hospital admissions

Answer

Total number of deaths due to all causes

Answer

Total number of deaths due to the disease concerned

Question 6

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

Accepted Answer

Distributed equally between study and control groups

Answer

Source of bias is interpretation

Answer

Associated both with exposure and disease

Answer

Independent risk factor for disease in question

Question 7

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:

Accepted Answer

1, 4, 5 and 7

Answer

1, 3, 5 and 8

Answer

2, 3, 6 and 7

Answer

2, 4, 5 and 8

Question 8

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

Accepted Answer

Total deaths in that year

Answer

Attributable deaths of a particular disease

Answer

Mid-year population during that year

Answer

Population at risk in that particular area

Question 9

Consider the following diseases:

1. Measles
2. Polio
3. Staphylococcal food poisoning
4. Typhoid Which of the above are the correct examples for incubation period of 10-14 days?

Accepted Answer

1 and 4

Answer

2 and 4

Answer

3 and 4

Answer

1 and 3

Question 10

When the prevalence rate is used without any qualification, it is taken to mean as

Accepted Answer

point prevalence rate

Answer

period prevalence rate

Answer

mean duration prevalence rate

Answer

annual prevalence rate

Epidemiology — MCQs

Epidemiology — MCQs

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