Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1741: Which research method is most appropriate for studying the progression of a disease over time?

A. Cohort Study (Correct Answer)
B. Cross sectional study
C. Randomized Control Trials
D. Interventional Studies

Explanation: ***Cohort Study*** - A **cohort study** observes a group of individuals over a period of time, allowing researchers to track the **natural progression of a disease** from exposure through onset and various stages. - This design is ideal for investigating the **incidence** of disease and identifying risk factors over time. *Cross sectional study* - A **cross-sectional study** assesses exposure and outcome at a **single point in time**, providing a snapshot. - It cannot establish temporality or observe disease progression, as it does not follow individuals over time. *Randomized Control Trials* - **Randomized controlled trials (RCTs)** are primarily designed to evaluate the **effectiveness of interventions** or treatments by comparing outcomes between an experimental group and a control group. - While they follow participants over time, their main goal is not to study the natural progression of an untreated disease. *Interventional Studies* - **Interventional studies** involve manipulating an exposure or treatment to observe its effect, often to test a hypothesis about a causal relationship. - While they track outcomes over time, their focus is on the impact of the intervention rather than the natural history or progression of a disease without intervention.

Question 1742: Which of the following is not an epidemiological indicator?

A. None of the options (Correct Answer)
B. ABER
C. Annual falciparum incidence
D. Annual parasite index

Explanation: ***None of the options*** - All listed options—**ABER (Annual Blood Examination Rate)**, **Annual parasite index**, and **Annual falciparum incidence**—are indeed widely recognized and utilized **epidemiological indicators**, particularly in the context of malaria surveillance and control. - As such, there is no option presented that is *not* an epidemiological indicator. *ABER* - **ABER (Annual Blood Examination Rate)** is an epidemiological indicator used to assess the annual number of blood smears examined per 1000 population. - It helps to measure the **intensity of surveillance** and case detection efforts in a given area for diseases like malaria. *Annual parasite index* - The **Annual Parasite Index (API)** is an epidemiological indicator that measures the number of confirmed malaria cases per 1000 population per year. - It is crucial for assessing **malaria endemicity** and the burden of the disease in a specific region. *Annual falciparum incidence* - **Annual falciparum incidence** is an epidemiological indicator specifically tracking the number of *Plasmodium falciparum* malaria cases per 1000 population per year. - This indicator is essential for monitoring the **severity and transmission of the most dangerous form of malaria**.

Question 1743: A person who has recovered from an infectious disease but continues to transmit the pathogen is best described as:

A. A person who acquires the microorganism due to his contact with the patient.
B. A person who acquires the microorganism from another carrier.
C. A person who is clinically recovered from an infectious disease but still capable of transmitting the infectious agent to others. (Correct Answer)
D. None of the options

Explanation: ***A person who is clinically recovered from an infectious disease but still capable of transmitting the infectious agent to others.*** - This definition accurately describes a **convalescent carrier**, who harbors an infectious agent without showing symptoms after recovery but can still transmit it. - This is a critical concept in **epidemiology** for understanding disease spread, contact tracing, and infection control measures. - Classic example: Typhoid Mary was a convalescent carrier of *Salmonella typhi* after recovering from typhoid fever. *A person who acquires the microorganism due to his contact with the patient.* - This describes a **secondary case** or **contact**, someone who has been exposed to a pathogen from an infected person. - It focuses on the mode of acquisition rather than the carrier state after recovery. - They may or may not develop disease or become carriers themselves. *A person who acquires the microorganism from another carrier.* - This describes the **mode of transmission** from an asymptomatic source (carrier-to-susceptible transmission). - It does not describe the epidemiological status of being a carrier after recovery. - The focus is on acquisition, not on the post-recovery transmission capability. *None of the options* - This statement is incorrect because the first option precisely defines a **convalescent carrier** as described in the question. - A person who has recovered but still transmits the pathogen is the classic definition of an asymptomatic carrier in the convalescent stage.

Question 1744: Which of the following is an example of population-based screening?

A. Diabetes mellitus screening for a 40-year-old male
B. Screening for immigrants from high-risk regions
C. Neonate screening for thyroid diseases (Correct Answer)
D. Pap smear for a 45-year-old female

Explanation: ***Neonate screening for thyroid diseases*** - This is a classic example of **population-based screening** because it targets an entire birth cohort (all newborns) for a specific set of conditions, regardless of individual risk factors. - The goal is to detect **congenital hypothyroidism** early to prevent severe, irreversible developmental consequences, making it a universal public health initiative. - This represents the **most comprehensive form** of population-based screening as it includes 100% of the target population. *Screening for immigrants from high-risk regions* - This is an example of **targeted screening** or selective screening, as it focuses on specific subgroups with identified elevated risk factors. - It's not population-based because it doesn't apply to the entire general population but rather to a defined group based on their origin or risk profile. *Diabetes mellitus screening for a 40-year-old male* - This would be considered **opportunistic screening** or case finding, often performed during routine check-ups based on age or other individual risk factors. - While some guidelines recommend screening for certain age groups, this is typically **risk-based** rather than universal population screening. *Pap smear for a 45-year-old female* - While organized cervical screening programs can be population-based when targeting all women in a defined age range, this option represents **age-specific** screening rather than universal screening. - The key distinction is that neonatal screening is more universally applied (all newborns) compared to age and gender-restricted programs, making it the **clearest example** of population-based screening in this list.

Question 1745: Which type of study is used to determine the cross product ratio?

A. Case control (Correct Answer)
B. Cohort
C. Cross sectional
D. RCT

Explanation: ***Case control*** - **Case-control studies** are specifically designed to compare exposure histories between individuals with a disease (cases) and those without (controls), which directly facilitates the calculation of the **odds ratio**. - The odds ratio is called the **cross-product ratio** because of its calculation method: (a×d)/(b×c), where the products are "crossed" in the 2×2 contingency table. - This is the **primary measure of association** in case-control studies and serves as an approximation of the relative risk, particularly for rare outcomes. *Cohort* - **Cohort studies** follow exposed and unexposed groups over time to determine the incidence of disease, allowing for the direct calculation of **relative risk** and **attributable risk**. - While odds ratios can be calculated from cohort data, the **relative risk** is the primary and preferred measure of association in cohort studies, not the cross-product ratio. *Cross sectional* - **Cross-sectional studies** assess the prevalence of disease and exposure at a single point in time, providing a snapshot of the population's health status. - They measure **prevalence** rather than incidence and can calculate prevalence ratios, but the term "cross-product ratio" specifically refers to the odds ratio from **case-control** study designs. *RCT* - **Randomized controlled trials (RCTs)** are experimental studies where participants are randomly assigned to intervention or control groups to evaluate treatment efficacy. - They primarily focus on determining the **relative risk** or **risk ratio** of an outcome following an intervention and are not designed for calculating the cross-product ratio (odds ratio) as used in observational case-control studies.

Question 1746: In a study of 200 patients, CA-125 testing was performed. Among the 100 patients who tested positive, 60 had ovarian cancer confirmed by histopathology. Among the 100 patients who tested negative, 20 had ovarian cancer confirmed by histopathology. What is the negative predictive value of this test?

A. 20/100
B. 40/100
C. 60/100
D. 80/100 (Correct Answer)

Explanation: ***80/100*** - The **negative predictive value (NPV)** is the probability that a patient who tests negative actually does not have the disease. - In this case, 100 patients tested negative, and 20 of them *did* have ovarian cancer, meaning 80 **did not** have ovarian cancer. Thus, NPV = 80/100. *20/100* - This represents the number of **false negatives** among all patients who tested negative, not the negative predictive value. - A false negative occurs when the test result is negative, but the disease is actually present. *40/100* - This value represents the number of patients who tested positive but **did not** have the disease (false positives), calculated as 100 (total positive tests) - 60 (true positives) = 40. - This is not the calculation for negative predictive value. *60/100* - This represents the number of **true positives** among all patients who tested positive. - This is a component of **positive predictive value**, not negative predictive value.

Question 1747: A researcher wanted to prove the relation between COPD and smoking. He collected patients records from government hospitals and records of cigarette sales from the finance and taxation department. This is an example of which study design:

A. Cross-sectional
B. Posological study
C. Ecological study (Correct Answer)
D. Operations research

Explanation: ***Ecological study*** - This study design involves analyzing data at a **population level**, rather than individual patient data. The researcher used aggregated data from hospital records (COPD prevalence) and cigarette sales (smoking rates) for populations or groups, not individual patients. - It examines the relationship between an exposure (smoking) and an outcome (COPD) by comparing disease frequencies in different populations with varying levels of exposure. *Cross-sectional* - A cross-sectional study measures the **prevalence** of a disease and exposure at a **single point in time** in individuals. - It does not involve comparing population-level aggregates or using secondary data from different sources to establish associations between population groups. *Posological study* - A posological study focuses on the **dosage** and administration of drugs, often to determine optimal therapeutic regimens. - This term is irrelevant to the described research design, which is concerned with the relationship between smoking and COPD. *Operations research* - Operations research is a discipline that applies analytical methods to improve **decision-making and efficiency** within organizations or systems. - This field is primarily concerned with optimizing processes and resource allocation, not establishing epidemiological associations between risk factors and diseases.

Question 1748: Confounding factor is defined as

A. Factor associated with exposure only and is distributed unequally in study and control groups.
B. Factor associated with both the exposure and the disease and is distributed equally in study and control groups
C. Factor associated with the disease and is distributed equally in study and control groups.
D. A factor that is associated with both the exposure and the disease, and is distributed unequally between study and control groups. (Correct Answer)

Explanation: ***A factor that is associated with both the exposure and the disease, and is distributed unequally between study and control groups.*** - A **confounding factor** is an **extraneous variable** that can influence both the **exposure** and the clinical **outcome** (disease), creating a spurious association. - Its **unequal distribution** between the exposure and control groups can distort the true relationship between the exposure and outcome, leading to biased results. *Factor associated with exposure only and is distributed unequally in study and control groups.* - This definition is incorrect because a confounding factor must also be associated with the **outcome (disease)**, not just the exposure. - If a factor is only associated with exposure, it might be an **intermediate variable** or simply a characteristic that differs between groups but doesn't independently affect the disease. *Factor associated with both the exposure and the disease and is distributed equally in study and control groups* - While a confounder is associated with both **exposure** and **disease**, if it is distributed **equally** between study and control groups, it will not bias the observed association between the exposure and the disease. - **Randomization** in clinical trials aims to distribute potential confounders equally, thereby reducing confounding. *Factor associated with the disease and is distributed equally in study and control groups.* - This definition is incomplete because a confounder must also be associated with the **exposure**, not just the disease. - If a factor is only associated with the disease and distributed equally, it might be a risk factor for the disease, but it won't distort the effect of the **primary exposure** of interest.

Question 1749: What is the definition of admission rate bias in epidemiological studies?

A. Selection bias due to reporting
B. No bias present
C. Bias in response rates
D. Bias occurring when probability of hospital admission is affected by both exposure and disease (Correct Answer)

Explanation: ***Bias occurring when probability of hospital admission is affected by both exposure and disease*** - **Admission rate bias**, also known as **Berkson's bias**, occurs when the **probability of admission** to a hospital is affected by both the exposure and the disease under study. - This bias can lead to a **spurious association** or a distorted measure of association between an exposure and a disease, as the observed rates within the hospital differ from those in the general population. - Commonly observed in **hospital-based case-control studies** where both cases and controls are drawn from hospitalized patients. *Selection bias due to reporting* - This describes **reporting bias**, where individuals may selectively report exposures or outcomes, leading to inaccuracies in data collection. - While a form of selection bias, it's distinct from admission rate bias where the selection mechanism is specifically tied to hospital admission. *No bias present* - This is incorrect as **admission rate bias** is a recognized form of selection bias that can significantly impact the validity of study findings. - Ignoring potential biases can lead to erroneous conclusions and misinterpretation of epidemiological data. *Bias in response rates* - This refers to **non-response bias**, which occurs when participants who respond to a study differ systematically from those who do not respond. - While a form of selection bias, it is different from admission rate bias, which is specific to how individuals are selected into a study cohort based on hospital admission.

Question 1750: 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**.

Practice by Chapter

Principles of Epidemiology

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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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