Measures of Disease Frequency — MCQs
Which of the following statements about incidence is false?
A new drug has been introduced into the market which was found to decrease mortality but it does not cure the disease. Which of the following is a true statement regarding prevalence and incidence?
Which of the following is the best parameter to predict virulence of acute infectious illness?
Which of the following factors can lead to an increase in the prevalence of a chronic disease in a population?
What is the definition of disease rate?
The difference between the incidence in the exposed and non-exposed group is best given by:
In a disease with 100% mortality, what is the relationship between incidence and prevalence?
Measure of communicability of a disease -
Population of a village on 1st January is 16,500. Since 1st January, 22 new cases of TB were detected during the year. Total registered cases were 220. What is the incidence of TB?
The incubation period of a disease is 5-14 days. What should be the quarantine period?
Measures of Disease Frequency Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following statements about incidence is false?
- A. Does not include unit of time (Correct Answer)
- B. It is a rate
- C. Numerator includes new cases
- D. Denominator includes population at risk
Explanation: ***Does not include unit of time*** - This statement is false because **incidence** is defined as the number of **new cases** of a disease over a specific period of time in a population at risk. - Therefore, it inherently includes a **unit of time** (e.g., per year, per month), making this option incorrect as a characteristic of incidence. *It is a rate* - **Incidence is a rate** because it quantifies the speed at which new cases of a disease occur within a population. - It expresses the number of new events (cases) per unit of population at risk over a specified time period. *Numerator includes new cases* - The **numerator of incidence** specifically counts the number of **new cases** of a disease that develop during a defined observation period. - This distinguishes it from prevalence, which includes all existing cases. *Denominator includes population at risk* - The **denominator for incidence** comprises the **population at risk** of developing the disease during the observation period. - Individuals who already have the disease or are immune are typically excluded from the denominator.
Question 2: A new drug has been introduced into the market which was found to decrease mortality but it does not cure the disease. Which of the following is a true statement regarding prevalence and incidence?
- A. Increase in prevalence (Correct Answer)
- B. Decrease in incidence
- C. Decrease in prevalence
- D. Increase in incidence
Explanation: ***Increase in prevalence*** - A drug that decreases mortality without curing the disease means people **live longer with the condition**, thus increasing the duration of disease - **Prevalence = Incidence × Duration**: Since duration increases while incidence remains constant, prevalence increases - More existing cases accumulate over time as fewer patients die from the disease *Decrease in incidence* - **Incidence** refers to the rate at which **new cases** develop in a population - This drug affects survival of existing cases, not the development of new cases - Since the drug neither prevents nor promotes new cases, **incidence remains unchanged** (not decreased) *Decrease in prevalence* - Prevalence would decrease if the drug **cured the disease** (removing people from the diseased pool) or if **mortality increased** - The scenario describes the opposite: decreased mortality without cure, which **increases** prevalence *Increase in incidence* - This would mean more new cases are developing over time - The drug affects **survival** of existing cases, not the **rate of new diagnoses** - Incidence remains unchanged, not increased
Question 3: Which of the following is the best parameter to predict virulence of acute infectious illness?
- A. Incidence
- B. Secondary attack rate
- C. Case fatality rate (Correct Answer)
- D. Crude death rate
Explanation: ***Case fatality rate*** - The **case fatality rate (CFR)** directly measures the **proportion of individuals diagnosed with a disease who die from it**, reflecting the pathogen's ability to cause death. - A higher CFR indicates greater **virulence** and a more severe disease outcome, making it the most direct predictor of an illness's ability to harm. *Incidence* - **Incidence** measures how often a disease occurs in a population over a specified period, indicating the **risk of contracting the disease**. - It does not provide information about the **severity** or **lethality** of the disease once contracted. *Secondary attack rate* - The **secondary attack rate** quantifies the probability that infection will occur among susceptible individuals within a particular group exposed to a primary case. - While it measures **transmissibility** and the potential for spread within a close group, it does not reflect the **virulence** or severity of the illness itself. *Crude death rate* - The **crude death rate** is the total number of deaths from all causes in a population over a given period, divided by the total population. - This parameter measures **overall mortality** in a population and is not specific to the deaths caused by a particular infectious illness, nor does it solely reflect its virulence.
Question 4: Which of the following factors can lead to an increase in the prevalence of a chronic disease in a population?
- A. Immigration of healthy persons
- B. Increased cure rate of disease
- C. Longer duration of illness (Correct Answer)
- D. Decrease in population
Explanation: ***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
Question 5: What is the definition of disease rate?
- A. Often expressed as a ratio or percentage
- B. Duration of disease occurrence in a specific timeframe
- C. Likelihood of developing a disease
- D. Frequency of disease occurrence in a population per unit of time (Correct Answer)
Explanation: ***Frequency of disease occurrence in a population per unit of time*** - A disease rate quantifies the **frequency** or **speed** at which disease events (new cases or existing cases) occur within a defined population over a specific time period. - It is a **measure of disease occurrence** that includes three essential components: the number of disease events (numerator), the population at risk (denominator), and a specified time period. - Examples include **incidence rate** (new cases per population per time) and **prevalence rate** (existing cases per population at a point in time). - Rates allow comparison of disease frequency across different populations and time periods. *Often expressed as a ratio or percentage* - While this is **technically correct** (rates are indeed ratios with numerator and denominator), this statement describes the **format** of presentation rather than the fundamental epidemiological concept. - This option focuses on **how** a rate is expressed, not **what** it measures or represents. *Duration of disease occurrence in a specific timeframe* - This refers to the **length of time** a disease persists, not the frequency of its occurrence. - **Duration** relates to concepts like disease course or chronicity, whereas a **rate** measures how often disease events happen. *Likelihood of developing a disease* - This defines **risk** or **probability**, which is related but distinct from a rate. - Risk represents the probability that an individual will develop disease over a specified period, while a rate measures the **speed or frequency** of disease occurrence in a population.
Question 6: The difference between the incidence in the exposed and non-exposed group is best given by:
- A. Attributable risk (Correct Answer)
- B. Population attributable risk
- C. Odds ratio
- D. Relative risk
Explanation: ***Attributable risk*** - **Attributable risk** (AR), also known as risk difference, directly quantifies the absolute difference in disease incidence between an **exposed group** and an **unexposed group**. - It represents the amount of disease incidence (or risk) in the exposed group that is **directly attributable to the exposure**, assuming a causal relationship. *Population attributable risk* - **Population attributable risk** (PAR) measures the proportion of disease incidence in the **total population** that is attributable to the exposure. - It takes into account both the impact of the exposure and the **prevalence of the exposure** in the population, which is distinct from simply comparing exposed and non-exposed groups. *Odds ratio* - The **odds ratio** (OR) is a measure of association between an exposure and an outcome, representing the **odds of an outcome occurring in the exposed group** compared to the odds of it occurring in the unexposed group. - It does not directly express the difference in incidence but rather the **ratio of odds**, often used in case-control studies. *Relative risk* - **Relative risk** (RR), or risk ratio, is the ratio of the **incidence of an outcome in the exposed group** to the incidence in the unexposed group. - It indicates how many times more likely an exposed group is to develop the outcome compared to an unexposed group, expressing a **ratio rather than a difference**.
Question 7: In a disease with 100% mortality, what is the relationship between incidence and prevalence?
- A. Prevalence is less than incidence (P < I) (Correct Answer)
- B. Prevalence equals incidence (P = I)
- C. There is no relationship between prevalence and incidence
- D. Prevalence is greater than incidence (P > I)
Explanation: ***Prevalence is less than incidence (P < I)*** - In a disease with 100% mortality, all affected individuals will eventually die, meaning their contribution to the **prevalent pool is temporary** or non-existent in the long run. - While new cases (incidence) continue to arise, the rapid removal of cases due to death prevents the buildup of prevalent cases, thus keeping prevalence lower than incidence. *Prevalence equals incidence (P = I)* - This scenario would imply that every new case immediately disappears or that the disease has no duration, which contradicts the concept of **disease progression** and death. - **Prevalence** is influenced by both the incidence rate and the duration of the disease; if duration is effectively zero due to immediate death, the relationship still leans towards prevalence being lower. *There is no relationship between prevalence and incidence* - This statement is incorrect as **incidence and prevalence are fundamentally linked**. Prevalence is a function of incidence and disease duration. - Changes in incidence directly affect **prevalence**, although the extent of this effect is modulated by factors like disease duration, recovery, or mortality. *Prevalence is greater than incidence (P > I)* - Prevalence being greater than incidence typically occurs in **chronic diseases** where individuals live with the condition for a long time, allowing prevalent cases to accumulate. - With **100% mortality**, individuals do not survive long enough to contribute significantly to the prevalent pool, making it impossible for prevalence to exceed incidence in this context.
Question 8: Measure of communicability of a disease -
- A. Sullivan index
- B. Incubation period
- C. Secondary attack rate (Correct Answer)
- D. Case fatality rate
Explanation: ***Secondary attack rate*** - This measures the **frequency of new cases** of a disease among contacts of known cases within a short period, reflecting how easily it spreads. - It specifically quantifies the **probability of infection** among susceptible individuals after exposure to a primary case. *Sullivan index* - The Sullivan index is a measure of **health expectancy**, specifically the number of years of life free of disability. - It is used in public health to assess the overall health status of a population, not disease communicability. *Incubation period* - The incubation period is the **time interval** between exposure to an infectious agent and the onset of clinical symptoms. - While important for understanding disease progression and isolation protocols, it does not directly measure the ease of transmission or communicability itself. *Case fatality rate* - The case fatality rate (CFR) indicates the **proportion of deaths** among individuals diagnosed with a specific disease. - It measures the **severity** of a disease, not how easily it spreads from person to person.
Question 9: Population of a village on 1st January is 16,500. Since 1st January, 22 new cases of TB were detected during the year. Total registered cases were 220. What is the incidence of TB?
- A. 100 per 100,000
- B. 133 per 100,000 (Correct Answer)
- C. 121 per 100,000
- D. 111 per 100,000
Explanation: ***133 per 100,000*** - The **incidence rate** calculates the frequency of new occurrences of a disease in a population over a specified time period. - It is calculated as (Number of new cases / Population at risk) * 100,000. Here, (22 / 16,500) * 100,000 = **133.33 per 100,000**. *100 per 100,000* - This value would be obtained if the number of new cases was 16.5 (16.5 / 16,500 * 100,000). - This calculation does not reflect the given number of **new cases (22)**. *121 per 100,000* - This value would be obtained if the number of new cases was 20 (20 / 16,500 * 100,000) or if the **population was different**. - This option does not match the actual data provided for the new cases and population. *111 per 100,000* - This value would be obtained if the number of new cases was approximately 18.3 (18.3 / 16,500 * 100,000). - It does not correctly reflect the **incidence calculation** based on the given number of 22 new cases.
Question 10: The incubation period of a disease is 5-14 days. What should be the quarantine period?
- A. 5 days
- B. 10 days
- C. 14 days (Correct Answer)
- D. 20 days
Explanation: ***14 days*** - The **quarantine period** should be equal to or slightly longer than the **maximum incubation period** of the disease. - In this case, 14 days covers the entire potential incubation range of 5-14 days, ensuring any exposed individual would develop symptoms within this period if infected. *5 days* - A 5-day quarantine period is too short as it is equal to the **minimum incubation period** and would not capture individuals with longer incubation times. - An individual could become symptomatic and transmit the disease after the 5-day quarantine if their incubation period was longer. *10 days* - A 10-day quarantine period is insufficient as it falls short of the **maximum incubation period** of 14 days. - An individual could still develop symptoms and become infectious up to 4 days after completing a 10-day quarantine. *20 days* - A 20-day quarantine period is unnecessarily long as it exceeds the **maximum incubation period**. - While it ensures coverage of the incubation period, it imposes excessive burden and resource utilization without added public health benefit.
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