Epidemiology — MCQs
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Which of the following statements is NOT true about a point source epidemic?
Which of the following is a true statement regarding longitudinal studies?
The comparison of mortality rates between two countries requires the application of direct standardization. Which of the following parameters makes it necessary to have standardization?
What does endemic disease mean?
Consistency of a screening test depends on
As per WHO guidelines, iodine deficiency disorders are considered endemic in the community when the prevalence of goitre in school-age children exceeds what percentage?
Specificity of a diagnostic test is defined as:
Attributable risk refers to which of the following?
What is the secondary attack rate in a household with 9 susceptible individuals, where 1 individual becomes infected initially and 2 additional individuals become infected 2 days later?
Which of the following is the primary epidemiological indicator for malaria?
Epidemiology Indian Medical PG Practice Questions and MCQs
Question 1831: Which of the following statements is NOT true about a point source epidemic?
- A. Explosive epidemic
- B. Only one peak
- C. No secondary waves
- D. Plateau phase (Correct Answer)
Explanation: ***Plateau phase*** (Correct Answer - This is NOT true) - A **plateau phase** is characterized by a sustained period of high incidence, which is typical of a **propagated epidemic** where transmission continues over time, **not a point source epidemic**. - In a point source epidemic, due to a single, brief exposure, the number of cases rises sharply and then falls quickly, typically **without a prolonged plateau**. - Point source epidemics show a **sharp rise and rapid fall**, reflecting the fact that all exposures occurred at approximately the same time. *Explosive epidemic* (True statement - not the answer) - This statement is **true** for a point source epidemic, as exposure to the common source often leads to a rapid increase in the number of cases over a short period. - The epidemic curve typically rises sharply and falls quickly, reflecting the **simultaneous exposure** of a large number of susceptible individuals. *Only one peak* (True statement - not the answer) - This statement is **true** for a point source epidemic, as all cases generally occur within one **incubation period** following a single common exposure, resulting in a single, distinct peak in the epidemic curve. - The single peak differentiates it from propagated epidemics, which can have multiple peaks reflecting successive generations of infection. *No secondary waves* (True statement - not the answer) - This statement is **true** for a point source epidemic because everyone exposed to the common source at the same time is infected, and there's no ongoing person-to-person transmission to create subsequent waves. - The epidemic curve will show cases occurring within one **incubation period** following the single exposure.
Question 1832: Which of the following is a true statement regarding longitudinal studies?
- A. Incidence rate can be calculated (Correct Answer)
- B. Studies natural history of disease
- C. Primarily designed to establish causation
- D. More time consuming than cross-sectional studies
Explanation: ***Correct: Incidence rate can be calculated*** - **Longitudinal studies** follow participants over time, allowing researchers to identify **new cases** of disease as they occur - Since the population at risk is followed prospectively, **incidence rates** (the rate at which new cases develop) can be accurately calculated - This is a **key advantage** that distinguishes longitudinal studies from cross-sectional studies, which can only calculate **prevalence** - Calculation of incidence is essential for understanding **disease risk** and evaluating **temporal relationships** between exposure and outcome *Studies natural history of disease* - While longitudinal studies CAN observe disease progression over time, this is not their most specific or defining characteristic - Many study designs (including case series and registry studies) can study natural history - **Natural history studies** are a specific subset of longitudinal studies, not a universal feature *Primarily designed to establish causation* - Longitudinal studies provide **evidence for temporal relationships** but are not primarily designed to establish causation - **Randomized controlled trials (RCTs)** are the gold standard for establishing causation through randomization and control of confounding variables - Longitudinal observational studies are subject to confounding and bias, limiting causal inference *More time consuming than cross-sectional studies* - While factually true, this describes a **limitation** rather than a defining characteristic or advantage - Many study designs are time-consuming; this is not specific to longitudinal studies - The question asks for a true statement that characterizes what longitudinal studies ARE or DO, not their practical constraints
Question 1833: The comparison of mortality rates between two countries requires the application of direct standardization. Which of the following parameters makes it necessary to have standardization?
- A. Numerators
- B. Denominators
- C. Causes of death
- D. Age distributions (Correct Answer)
Explanation: ***Age distributions*** - **Direct standardization** is crucial when comparing mortality rates between populations with different **age structures**. A population with a larger proportion of older individuals will naturally have a higher crude mortality rate regardless of underlying health. - By standardizing for age, we can remove the confounding effect of age and get a more accurate comparison of **disease burden** or **healthcare effectiveness**. *Numerators* - The numerator in mortality rates typically represents the **number of deaths**, which is a direct count and does not inherently require standardization to be understood. - While the numerator is essential for calculating the rate, its raw value doesn't introduce bias in comparison as much as population characteristics. *Denominators* - The denominator represents the **total population at risk**, which is used in calculating crude mortality rates. - While vital for rate calculation, the denominator itself doesn't directly cause a need for standardization; rather, the **composition** of the denominator (e.g., age groups) is the critical factor. *Causes of death* - While comparing **specific causes of death** can be informative, the "cause of death" itself does not necessitate overall mortality rate standardization. - Standardization focuses on population characteristics (like age) that influence the overall likelihood of death, not the specific etiology.
Question 1834: What does endemic disease mean?
- A. Occurs clearly in excess of normal expectancy
- B. Exhibits seasonal pattern
- C. Is prevalent among animals
- D. Is consistently present in a specific population or geographic area (Correct Answer)
Explanation: ***Is consistently present in a specific population or geographic area*** - An **endemic disease** is one that is always present within a given population or geographical area at expected levels. - The disease's continuous presence implies a **stable baseline frequency** within that region. *Occurs clearly in excess of normal expectancy* - This definition describes an **epidemic**, which is a sudden increase in the number of cases of a disease above what is normally expected in that population or area. - It signifies a **deviation from the expected endemic level**, indicating an outbreak. *Exhibits seasonal pattern* - While some endemic diseases can show **seasonal variations** (e.g., flu in winter), this characteristic alone does not define endemicity. - A seasonal pattern primarily describes the **timing of outbreaks** or peaks, rather than the disease's constant presence. *Is prevalent among animals* - This describes a **zoonotic disease** if it can also be transmitted to humans. - The term **epizootic** is used to describe an outbreak of disease in an animal population, which is distinct from the human population concept of endemicity.
Question 1835: Consistency of a screening test depends on
- A. Accuracy (overall correctness of the test)
- B. Reliability (Correct Answer)
- C. Sensitivity (correctly identifies those with the disease)
- D. Specificity (correctly identifies those without the disease)
Explanation: ***Reliability*** - The **consistency** of a screening test refers to its ability to produce the same results when repeated under the same conditions. This characteristic is known as **reliability** or reproducibility. - A reliable test minimizes **random error**, ensuring that variations in results are due to actual changes in the individual rather than testing inaccuracies. *Accuracy (overall correctness of the test)* - **Accuracy** refers to how close a test result is to the **true value**, which is a measure of validity, not solely consistency. - A test can be reliable (consistent) but not accurate, meaning it consistently produces the same incorrect results. *Sensitivity (correctly identifies those with the disease)* - **Sensitivity** is the proportion of true positives that are correctly identified by the test, indicating its ability to correctly identify individuals *with* the disease. - This is a measure of the test's **validity** in detecting disease, not its consistency over repeated measurements. *Specificity (correctly identifies those without the disease)* - **Specificity** is the proportion of true negatives that are correctly identified by the test, indicating its ability to correctly identify individuals *without* the disease. - This is also a measure of the test's **validity** in ruling out disease, rather than its consistency when repeated.
Question 1836: As per WHO guidelines, iodine deficiency disorders are considered endemic in the community when the prevalence of goitre in school-age children exceeds what percentage?
- A. 5% (Correct Answer)
- B. 10%
- C. 15%
- D. 1%
Explanation: ***5%*** - According to **WHO guidelines**, iodine deficiency disorders are considered **endemic** when the prevalence of goitre in school-age children **exceeds 5%**. - This is the **specific threshold** established by WHO to classify a community as having endemic iodine deficiency requiring public health intervention. - School-age children (6-12 years) are used as the indicator population because they are the most sensitive group for detecting iodine deficiency. *1%* - This percentage is **below the WHO threshold** of 5% for defining endemic iodine deficiency. - A prevalence of 1% indicates mild iodine insufficiency but does not meet the criteria for endemicity requiring immediate widespread intervention. *10%* - While 10% prevalence certainly indicates a **moderate to severe public health problem**, this is not the WHO threshold for defining endemicity. - The threshold is **5%, not 10%** - any prevalence exceeding 5% (including 10%) would be classified as endemic. *15%* - This represents a **severe iodine deficiency problem**, but it is not the WHO threshold percentage. - The correct threshold is **5%** - both 10% and 15% exceed this threshold and would be classified as endemic, but they are not the defining cutoff point.
Question 1837: Specificity of a diagnostic test is defined as:
- A. 0.95 (Correct Answer)
- B. 0.05
- C. 0.4
- D. 0.8
Explanation: ***0.95*** - **Specificity** is the proportion of individuals without disease who test negative, calculated as **TN/(TN+FP)**. - A specificity of 0.95 (95%) indicates an excellent test that correctly identifies 95% of healthy individuals as negative. *0.05* - This value represents the **false positive rate** (1 - specificity), not specificity itself. - A specificity of 0.05 would mean only 5% of healthy individuals test negative, indicating a very poor test. *0.4* - This value is too low for specificity and could represent other test parameters like **positive predictive value**. - A specificity of 0.4 would incorrectly classify 60% of healthy individuals as positive, making the test clinically unreliable. *0.8* - This value typically represents **sensitivity**, which is the proportion of diseased individuals who test positive. - **Sensitivity** is calculated as **TP/(TP+FN)**, which is different from specificity that focuses on healthy individuals.
Question 1838: Attributable risk refers to which of the following?
- A. Fatality of a disease.
- B. Disease risk ratio between exposed and non-exposed.
- C. Communicability of a disease.
- D. Risk difference between exposed and unexposed populations. (Correct Answer)
Explanation: ***Risk difference between exposed and unexposed populations.*** - **Attributable risk (AR)**, also known as **risk difference**, quantifies the absolute difference in disease incidence (or risk) between an exposed group and an unexposed group. - It represents the amount of disease risk that can be directly attributed to the exposure, which could theoretically be prevented if the exposure were eliminated. - Formula: AR = Incidence in exposed - Incidence in unexposed *Fatality of a disease.* - The **fatality of a disease** is measured by the **case fatality rate (CFR)**, which indicates the proportion of individuals diagnosed with a disease who die from it. - This is a measure of disease severity, not the incremental risk due to an exposure. *Disease risk ratio between exposed and non-exposed.* - The **disease risk ratio** (or **relative risk, RR**) compares the incidence of disease in an exposed group to the incidence in an unexposed group as a ratio. - Formula: RR = (Incidence in exposed) / (Incidence in unexposed) - While it measures the strength of association, it does not represent the absolute amount of risk attributable to the exposure. *Communicability of a disease.* - The **communicability of a disease** refers to its ability to spread from one individual to another, often measured by metrics like the **basic reproduction number (R₀)**. - This concept is related to infectious disease transmission dynamics, not the attributable risk of a specific exposure.
Question 1839: What is the secondary attack rate in a household with 9 susceptible individuals, where 1 individual becomes infected initially and 2 additional individuals become infected 2 days later?
- A. 50%
- B. 65%
- C. 25% (Correct Answer)
- D. 33%
Explanation: ***25%*** - The secondary attack rate is calculated as **(Number of secondary cases / Total number of susceptible contacts) * 100**. - In this scenario, there are 2 new cases among 8 susceptible contacts (initially 9 susceptible, minus the 1 primary case). So, (2 / 8) * 100 = **25%**. *33%* - This percentage would be relevant if there were 2 secondary cases out of 6 susceptible individuals, which is not the case here. - This calculation misrepresents the denominator by not correctly accounting for the initial prevalent case. *50%* - This would imply 2 secondary cases out of 4 susceptible individuals, which is not consistent with the given problem. - It would overestimate the secondary attack rate based on the provided numbers. *65%* - This percentage is significantly higher than what the given data suggests for the secondary attack rate. - It does not correspond to the calculation of 2 secondary cases among 8 susceptible individuals.
Question 1840: Which of the following is the primary epidemiological indicator for malaria?
- A. Annual falciparum incidence
- B. Annual parasite incidence (Correct Answer)
- C. Annual blood examination rate
- D. Annual incidence of malaria cases
Explanation: ***Annual parasite incidence*** - **Annual parasite incidence (API)** refers to the number of confirmed malaria cases per 1,000 population per year in a given area. - It is a **key epidemiological indicator** used to assess the burden of malaria and track trends over time, providing a direct measure of disease occurrence. *Annual falciparum incidence* - This indicator focuses specifically on **_Plasmodium falciparum_ infections**, which are often the most severe form of malaria. - While important, it does not encompass all malaria species and therefore provides a less comprehensive measure of the overall malaria burden compared to API. *Annual blood examination rate* - The **annual blood examination rate (ABER)** indicates the number of blood slides examined for malaria per 1,000 population per year. - It is a measure of **surveillance effort** and access to diagnostic testing, rather than a direct measure of malaria incidence. *Annual incidence of malaria cases* - While this phrase describes generally what an epidemiological indicator for malaria would measure, it is less specific and a less commonly used standardized term than **Annual Parasite Incidence (API)**. - The term **API** is universally recognized and has a precise definition related to confirmed parasite-positive cases per 1,000 population.
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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