Epidemiology Practice Questions

Q: Which of the following factors can lead to an increase in the prevalence of a chronic disease in a population?

Longer duration of illness. ***Longer duration of illness*** - Prevalence is determined by the formula: **Prevalence = Incidence × Duration** - A longer duration of illness means individuals live longer with the disease, increasing the pool of existing cases at any given time - Even if incidence remains constant, increased duration (due to improved survival or slower disease progression) directly increases prevalence *Immigration of healthy persons* - Immigration of healthy individuals increases the denominator (total population) without increasing the numerator (disease cases) - This dilutes the proportion of diseased individuals, thereby **decreasing prevalence** *Increased cure rate of disease* - Higher cure rates remove individuals from the pool of existing cases more rapidly - This shortens the effective duration of disease in the population, thereby **decreasing prevalence** *Decrease in population* - A general population decrease would only increase prevalence if healthy individuals selectively left or died at higher rates than diseased individuals - In most scenarios, population decrease affects both groups proportionally and does not predictably increase prevalence - This is not a recognized factor for increasing prevalence in epidemiological principles

Q: What is the structure of the ICD-10 classification system?

Arranged in 3 volumes. ***Arranged in 3 volumes*** - The **ICD-10 classification system** is traditionally published in **three volumes** for ease of use. - **Volume 1** lists diseases alphabetically, **Volume 2** provides instructional and guidelines, and **Volume 3** has an alphanumeric index. *Revised every 10 years* - ICD classifications are revised periodically, but there is **no fixed 10-year revision cycle**; updates occur as needed. - For instance, ICD-9 was in use for many decades before ICD-10 and then ICD-11 was released significantly later. *Consists of 22 chapters* - The ICD-10 classification system is organized into **21 chapters**, each covering a specific range of diseases or health problems. - These chapters categorize diseases and conditions based on criteria such as etiology, body system, or type of injury. *Produced by the World Health Organization* - The **World Health Organization (WHO)** is indeed responsible for developing and maintaining the ICD system. - However, this option describes the **originator** of the system, not its structural arrangement.

Q: Which of the following is false about longitudinal studies?

Easy to organize and less time consuming. ***Easy to organize and less time consuming*** - Longitudinal studies involve **following subjects over a long period**, often many years, making them inherently time-consuming. - They also require **significant resources** for participant recruitment, retention, and data collection, making them complex to organize. *Helps us study natural history of a disease* - Longitudinal studies track individuals over time, allowing researchers to observe the **progression of a disease** from its onset through various stages. - This design is crucial for understanding how diseases develop and change without intervention. *Helps in identification of risk factors of a disease* - By following individuals before disease onset, longitudinal studies can identify **exposures or characteristics** that precede and predict the development of a disease. - This allows for the establishment of **temporal relationships** between risk factors and outcomes. *Helps us find out rate of occurrence of new cases of a disease* - Longitudinal studies are essential for calculating **incidence rates**, which measure the rate at which new cases of a disease occur in a population at risk over a specified period. - They involve following a population free of the disease initially and then observing who develops the disease.

Q: Smallpox eradication was declared by WHO in 1980. All of the following epidemiological factors had a role in the eradication of smallpox, except:

Cross-immunity from other animal poxviruses. ***Cross-immunity from other animal poxviruses*** - This was **NOT** a factor in smallpox eradication and is the correct answer to this "except" question. - The *Variola virus* (which causes smallpox) infected **only humans** - there was no significant animal reservoir. - **No cross-immunity** existed from other animal poxviruses that would have contributed to population-level immunity. - The **absence of zoonotic transmission** (animal-to-human spread) actually *helped* eradication efforts, as eliminating the virus from the human population meant complete eradication. *Low rate of asymptomatic transmission* - The **highly symptomatic nature** of smallpox meant that infected individuals were easily identifiable, allowing for targeted isolation and vaccination. - This limited the spread of the virus by **undetected carriers**, which is a significant challenge for diseases with high rates of asymptomatic spread. - Visible pustular rash made **case detection** straightforward for surveillance programs. *Vaccine was highly effective* - The **vaccinia virus vaccine** provided robust and long-lasting protection against smallpox with a single dose. - Its effectiveness in preventing disease and transmission was central to the success of **ring vaccination strategies** and mass immunization campaigns. - High vaccine efficacy (>95%) meant that vaccination efforts could break transmission chains effectively. *Life-long immunity* - Both natural infection and successful vaccination conferred **long-lasting, often life-long, immunity** to smallpox. - This meant that vaccinated individuals or those who had recovered from the disease did not remain susceptible, preventing **reinfection** and reducing the pool of susceptible hosts over time. - Durable immunity eliminated the need for repeated vaccination campaigns in already-protected populations.

Q: In the context of a cohort study, which of the following statistical measures is not typically used?

Odds ratio. ***Odds ratio*** - The **odds ratio** is primarily used in **case-control studies** to estimate the association between exposure and outcome. - While it can be calculated in a cohort study, it is not the most appropriate or typical measure of association, as the **relative risk** can be directly calculated. *Incidence rate* - **Incidence rate** is a measure reflecting the **rate at which new cases** of a disease or health condition occur in a population at risk over a specified period. - It is a fundamental measure in cohort studies to quantify the **risk of developing an outcome** in exposed versus unexposed groups. *Attributable risk percentage* - The **attributable risk percentage** quantifies the proportion of disease in the exposed group that is **attributable to the exposure**. - This measure helps determine the public health impact of an exposure in a cohort study. *Relative risk* - The **relative risk** (also called risk ratio) directly compares the incidence of disease in the exposed group to the incidence in the unexposed group. - It is the **primary measure of association** calculated in cohort studies, indicating how many times more likely an exposed group is to develop the outcome compared to an unexposed group.

Q: Which one of the following is a good index of the severity of an acute disease?

Case fatality rate. ***Case fatality rate*** - The **case fatality rate (CFR)** is the proportion of individuals diagnosed with a disease who die from that disease within a specified time period. - It directly reflects the **virulence** or **severity** of an acute disease by measuring the proportion of fatal outcomes among confirmed cases. *Cause specific death rate* - This measures the **number of deaths** from a specific cause per unit of population during a specified period. - It reflects the **overall burden** of a disease in a population, but not necessarily the severity among those who contract it. *Standardized mortality ratio* - The **standardized mortality ratio (SMR)** compares the observed number of deaths in a study population to the expected number of deaths if the study population had the same age-specific rates as a standard population. - SMR is used to assess the **overall mortality experience** of a group, adjusting for age, but not specifically the severity of an acute disease in affected individuals. *Five year survival* - **Five-year survival rate** is the percentage of people who are still alive five years after being diagnosed with a disease. - It is primarily used for **chronic diseases**, particularly cancers, to assess long-term prognosis rather than the immediate severity of an acute illness.

Q: Which of the following is a type of observational study that analyzes population-level data?

Ecological study. ***Ecological study*** - This type of study examines the relationship between an exposure and an outcome at the **population level** rather than the individual level. - It often uses aggregated data, such as incidence rates of disease in different geographic areas, to identify associations. *Case-control study* - This is an **individual-level observational study** that compares individuals with a disease (cases) to individuals without the disease (controls) and looks back retrospectively at their exposures. - It is used to investigate potential risk factors for a disease but does not analyze population-level data directly. *Randomized controlled trial* - This is an **experimental study design** where participants are randomly assigned to an intervention group or a control group. - It is considered the gold standard for establishing causality but does not analyze observational population-level data. *Longitudinal study* - This is an **individual-level observational study** that follows the same group of individuals over a period of time, collecting data at multiple points. - While it observes changes over time, it typically focuses on individual-level trends and outcomes, not aggregated population data.

Question 1

Which of the following factors can lead to an increase in the prevalence of a chronic disease in a population?

Accepted Answer

Longer duration of illness

Answer

Immigration of healthy persons

Answer

Increased cure rate of disease

Answer

Decrease in population

Question 2

What is the structure of the ICD-10 classification system?

Accepted Answer

Arranged in 3 volumes

Answer

Consists of 21 chapters

Answer

Revised every 10 years

Answer

Produced by the World Health Organization

Question 3

Which of the following is false about longitudinal studies?

Accepted Answer

Easy to organize and less time consuming

Answer

Helps us study natural history of a disease

Answer

Helps in identification of risk factors of a disease

Answer

Helps us find out rate of occurrence of new cases of a disease

Question 4

Smallpox eradication was declared by WHO in 1980. All of the following epidemiological factors had a role in the eradication of smallpox, except:

Accepted Answer

Cross-immunity from other animal poxviruses

Answer

Life-long immunity

Answer

Vaccine was highly effective

Answer

Low rate of asymptomatic transmission

Question 5

In the context of a cohort study, which of the following statistical measures is not typically used?

Accepted Answer

Odds ratio

Answer

Incidence rate

Answer

Attributable risk percentage

Answer

Relative risk

Question 6

Which one of the following is a good index of the severity of an acute disease?

Accepted Answer

Case fatality rate

Answer

Cause specific death rate

Answer

Standardized mortality ratio

Answer

Five year survival

Question 7

Which of the following is a type of observational study that analyzes population-level data?

Accepted Answer

Ecological study

Answer

Case-control study

Answer

Randomized controlled trial

Answer

Longitudinal study

Question 8

In epidemiology, generation time is defined as:

Accepted Answer

The interval of time between the receipt of infection by host and maximal infectivity of the host.

Answer

The interval of time between the receipt of infection by host and the appearance of first sign or symptom of the disease.

Answer

The interval between the receipt of infection and the onset of symptoms.

Answer

The interval of time between successive cases in a chain of transmission.

Question 9

Demographic gap refers to:

Accepted Answer

Disparity between the number of births and deaths in a population

Answer

Disparity in the population size of males and females

Answer

Disparity in age-specific birth and death rates

Answer

Disparity in life expectancy between males and females

Question 10

An investigator is studying a new biomarker test to detect breast cancer at early stages. A randomized study is conducted to compare the new test to the current standard of care, mammography, among women over 50 years old. They conclude that breast cancer patients whose cancer was identified by the biomarker lived on average 1.5 years longer than those whose cancers were identified by mammography. If additional independent studies show that there truly was no difference in survival between the two groups, which of the following biases is most likely to have occurred?

Accepted Answer

Lead time bias

Answer

Confounding bias

Answer

Test insensitivity

Answer

Measurement error

Epidemiology — MCQs

Epidemiology — MCQs

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