Epidemiology Practice Questions

Q: The amount of previously unrecognized disease that is diagnosed as a result of the screening effort is known as :

Yield. ***Yield*** - The **yield** of a screening program refers to the amount of **previously unrecognized disease** that is identified through the screening effort. - It essentially measures the **productivity** or **effectiveness** of the screening intervention in detecting new cases. *Reliability* - **Reliability** refers to the **consistency** of a measurement or test, meaning it produces the same results under the same conditions. - It does not describe the amount of new disease found but rather the **reproducibility** of the screening process. *Predictive accuracy* - **Predictive accuracy** (positive predictive value or negative predictive value) indicates the probability that a positive or negative test result **truly reflects** the presence or absence of the disease. - While related to screening performance, it's a measure of how accurately the test predicts disease status, not the overall quantity of newly diagnosed disease. *Validity* - **Validity** refers to the extent to which a test measures what it is intended to measure, encompassing both **sensitivity** and **specificity**. - It describes the **accuracy** of the test in correctly identifying diseased and non-diseased individuals, but not the total number of new cases identified in the population.

Q: In disability rates, event type indicators are the following except

Limitation of activity. ***Limitation of activity*** - While related to disability measurement, **limitation of activity** is typically classified as a **chronic disability indicator** or **impact indicator** rather than an event type indicator measured in discrete time units. - Event type indicators usually quantify disability in **specific time units (days)** representing acute episodes or events. - **Limitation of activity** describes a long-term functional status rather than countable discrete events. *Work loss days* - **Work loss days** are a standard **event type indicator** measuring days of work lost due to illness or injury. - This is a specific type of restricted activity day for the employed population. - Quantifies disability impact in discrete, countable time units (days). *Bed disability days* - **Bed disability days** directly measure severe disability events where an individual is confined to bed. - This is a classic **event type indicator** used in national health surveys. - Represents the most severe form of restricted activity days. *Number of days of restricted activity* - **Restricted activity days** are the primary **event type indicator** in disability measurement. - Quantifies days when usual activities are limited due to health conditions. - This is the broadest category of event type indicators, encompassing bed disability days and work loss days.

Q: The Relative Risk of a disease measures the

Strength of association between suspected cause and effect. ***Strength of association between suspected cause and effect*** - **Relative Risk (RR)** quantifies how much more likely an exposed group is to develop an outcome compared to an unexposed group, directly indicating the **strength of association**. - An RR of 1 means no association, an RR > 1 suggests increased risk, and an RR < 1 suggests protection, demonstrating the **magnitude of the relationship**. *Biological plausibility between suspected cause and effect* - **Biological plausibility** refers to the coherence of a hypothesis with existing biological and medical knowledge. - While it's a criterion for causal inference, **Relative Risk** itself measures statistical association, not the underlying biological mechanism. *Temporal relationship between suspected cause and effect* - The **temporal relationship** (cause precedes effect) is a crucial criterion for causality but is not directly measured by **Relative Risk**. - **Relative Risk** evaluates risk at a given point or over a period, assuming exposure has already occurred. *Specificity of association between suspected cause and effect* - **Specificity of association** suggests that a single exposure is linked to a single disease, which is rarely true in complex biological systems. - **Relative Risk** quantifies association without implying one-to-one causation or absence of other contributing factors.

Q: Case Fatality Rate of a disease is a measure of its

Virulence. ***Virulence*** - **Case fatality rate (CFR)** is defined as the proportion of persons with a disease who **die from that disease**. - It directly reflects the **severity** or **lethality** of a disease among those infected. - A higher CFR indicates that the disease is more **virulent**, causing a greater proportion of infected individuals to die. - CFR is the standard epidemiological measure of **virulence**. *Chronicity* - **Chronicity** refers to the **duration** of a disease, indicating whether it is long-lasting or recurrent. - It does not directly measure the disease's ability to cause death among those infected. *Endemicity* - **Endemicity** describes the **constant presence** and/or usual prevalence of a disease in a geographic area or population. - This term relates to the typical occurrence pattern, not the deadliness of the disease. *Infectivity* - **Infectivity** is the ability of an organism to **cause infection** in a susceptible host. - It measures how easily an agent can spread and establish itself, not its capacity to cause severe disease or death.

Q: "Mid-year population" is not the denominator of which mortality rate?

Proportional mortality rate. ***Proportional mortality rate*** - The **proportional mortality rate** uses the **total number of deaths from all causes** as its denominator, not the mid-year population. - It expresses the proportion of all deaths due to a specific cause, rather than a rate per population at risk. - Formula: PMR = (Deaths from specific cause / Total deaths) × 100 *Age specific death rate* - The **age-specific death rate** uses the **mid-year population of a specific age group** as its denominator to calculate the number of deaths within that group. - This allows for comparison of mortality across different age cohorts. *Crude death rate* - The **crude death rate** uses the **total mid-year population** of a given area as its denominator. - It represents the overall mortality experience of a population but does not account for age structure. *Weekly death rate* - Though not a standard epidemiological measure, if calculated, this would use the **mid-week or average population for that specific week** as its denominator. - This would measure mortality frequency over a shorter, defined period using a population base.

Q: Consider the following characteristics of biological agents : 1. Infectivity 2. Pathogenicity 3. Virulence 4. Communicability Among the above characteristics, which are used to measure the ability of biological agents to induce clinically apparent illness?

2 and 3. ***2 and 3*** - **Pathogenicity** is the ability of an infectious agent to cause disease (clinically apparent illness) in infected individuals, measured as the proportion of infected persons who develop clinical disease. - **Virulence** is the ability of an agent to produce severe disease, measured as the proportion of clinical cases that are severe or fatal. - **Both characteristics measure different aspects of the ability to induce clinically apparent illness**: pathogenicity measures whether clinical illness occurs, while virulence measures the severity of that clinical illness. - Together, they comprehensively describe an agent's capacity to produce clinically apparent disease. *2 only* - While pathogenicity does measure the ability to cause clinically apparent illness, this is incomplete. - Virulence is also a measure of the ability to induce clinically apparent illness, specifically measuring the severity spectrum of that illness. *3 only* - Virulence alone is insufficient as it only measures severity among those who are already clinically ill. - Pathogenicity is also needed to measure the ability to produce clinical illness in the first place. *1 and 2* - **Infectivity** measures the ability of an agent to enter, survive, and multiply in a host, which is a prerequisite for disease but does not measure clinical illness itself. - An agent can have high infectivity but low pathogenicity (causing mostly subclinical infections). - Only pathogenicity and virulence directly measure aspects of clinically apparent illness.

Q: "Risk ratio" is also known as:

Relative risk. ***Relative risk*** - **Risk ratio** is another term for **relative risk**, which is a measure of association between exposure to a factor and the risk of an outcome. - It compares the risk of an event in an **exposed group** to the risk of an event in an **unexposed group**. *Odds ratio* - The **odds ratio** is a measure of association that quantifies the relationship between an exposure and an outcome, often used in **case-control studies**. - It approximates the relative risk when the outcome is **rare** but is distinct in its calculation based on odds rather than risks. *Attributable risk* - **Attributable risk** (or risk difference) quantifies the **absolute difference in risk** between exposed and unexposed groups. - It represents the amount of disease incidence that can be directly attributed to the exposure. *Population attributable risk* - **Population attributable risk** is the proportion of a disease in the total population that is attributable to a specific exposure. - It considers both the **strength of the association** and the **prevalence of the exposure** in the population.

Q: Consider the following criteria for a "screening test" : 1. Disease should have a latent period 2. Condition (disease) should be rare 3. Disease should be amenable to treatment Which of the above must be satisfied before including a screening test into any programme?

1 and 3. ***1 and 3*** - A successful screening program requires the disease to have a detectable **latent period** (criterion 1) during which early intervention can be beneficial. - Furthermore, the disease must be **amenable to treatment** (criterion 3); if there's no effective treatment, early detection offers no clinical advantage. *1 only* - While a **latent period** is essential for effective screening, it is not the sole criterion; the availability of treatment is equally critical. - Screening for a disease with a latent period but no effective treatment would lead to early diagnosis without improved outcomes, causing unnecessary anxiety. *2 only* - The **rarity of a condition** (criterion 2) is generally not a prerequisite for screening; in fact, screening is often more cost-effective for more prevalent diseases. - Screening rare diseases can lead to a low positive predictive value and higher rates of false positives, making it inefficient without substantial public health impact. *1 and 2* - Although a **latent period** is necessary, screening is generally more useful and cost-effective for diseases that are common enough to warrant population-level intervention, not necessarily rare diseases. - Screening primarily aims for early intervention and improved outcomes, which are not solely dependent on rarity, but on the disease's burden and treatability.

Q: A new drug is to be evaluated for its therapeutic effect. The best study design will be.

Randomized controlled trial. ***Randomized controlled trial*** - This design is the **gold standard** for evaluating the effectiveness of a new therapeutic intervention. - **Randomization** minimizes confounding, and a control group allows for direct comparison of outcomes, isolating the **drug's effect**. *Natural experiment* - This design involves observing the effects of an intervention that occurs naturally, without researcher manipulation. - It lacks the **control** and **randomization** necessary to definitively attribute observed effects solely to the therapeutic agent. *Cross sectional survey* - This design assesses the prevalence of a condition or exposure at a single point in time. - It cannot establish **causality** or evaluate the therapeutic effect of an intervention over time. *Case control design* - This retrospective design compares individuals with a disease (cases) to those without (controls) to identify past exposures. - It is used to investigate **risk factors** for diseases, not to evaluate the therapeutic efficacy of a new drug.

Question 1

The amount of previously unrecognized disease that is diagnosed as a result of the screening effort is known as :

Accepted Answer

Yield

Answer

Reliability

Answer

Predictive accuracy

Answer

Validity

Question 2

Which one of the following formulae is used for computing the Aedes aegypti Index at International Airports and sea ports ?

Accepted Answer

Number of containers positive for Aedes aegypti breeding / Total number of containers x 100

Answer

Number of houses positive for Aedes aegypti breeding / Total number of houses x 100

Answer

Number of bites of Aedes aegypti / Total number of man hours x 100

Answer

Number of containers positive for Aedes aegypti breeding / Total number of houses x 100

Question 3

In disability rates, event type indicators are the following except

Accepted Answer

Limitation of activity

Answer

Work loss days

Answer

Bed disability days

Answer

Number of days of restricted activity

Question 4

The Relative Risk of a disease measures the

Accepted Answer

Strength of association between suspected cause and effect

Answer

Biological plausibility between suspected cause and effect

Answer

Temporal relationship between suspected cause and effect

Answer

Specificity of association between suspected cause and effect

Question 5

Case Fatality Rate of a disease is a measure of its

Accepted Answer

Virulence

Answer

Chronicity

Answer

Endemicity

Answer

Infectivity

Question 6

"Mid-year population" is not the denominator of which mortality rate?

Accepted Answer

Proportional mortality rate

Answer

Age specific death rate

Answer

Crude death rate

Answer

Weekly death rate

Question 7

Consider the following characteristics of biological agents :

1. Infectivity
2. Pathogenicity
3. Virulence
4. Communicability

Among the above characteristics, which are used to measure the ability of biological agents to induce clinically apparent illness?

Accepted Answer

2 and 3

Answer

3 only

Answer

2 only

Answer

1 and 2

Question 8

"Risk ratio" is also known as:

Accepted Answer

Relative risk

Answer

Odds ratio

Answer

Attributable risk

Answer

Population attributable risk

Question 9

Consider the following criteria for a "screening test" :

1. Disease should have a latent period
2. Condition (disease) should be rare
3. Disease should be amenable to treatment Which of the above must be satisfied before including a screening test into any programme?

Accepted Answer

1 and 3

Answer

1 only

Answer

2 only

Answer

1 and 2

Question 10

A new drug is to be evaluated for its therapeutic effect. The best study design will be.

Accepted Answer

Randomized controlled trial

Answer

Natural experiment

Answer

Cross sectional survey

Answer

Case control design

Epidemiology — MCQs

Epidemiology — MCQs

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