Analytical Epidemiology — MCQs
A study that examines individuals who have already contracted a disease to identify risk factors is called:
In the context of a cohort study, which of the following statistical measures is not typically used?
Berksonian bias is a type of ?
According to Hill's criteria, which of the following is NOT a criterion for establishing causality in noncommunicable diseases?
The difference between the incidence in the exposed and non-exposed group is best given by:
A 10-year long study concerning the use of fluorides and pit and fissure sealants in the control of caries on the same population group is an example of:
What is the primary purpose of interventional studies in clinical research?
What is the definition of Population Attributable Risk?
A new test was developed for detection of COVID-19. What is the sensitivity of the test as per the information provided above?
Which of the following Screening methods for Disease is the least useful?
Analytical Epidemiology Indian Medical PG Practice Questions and MCQs
Question 1: A study that examines individuals who have already contracted a disease to identify risk factors is called:
- A. Control cohort
- B. Cohort
- C. Cross-sectional
- D. Case control (Correct Answer)
Explanation: ***Case control*** - A **case-control study** specifically examines individuals who have already contracted the disease (**cases**) and compares them to those without the disease (**controls**). - The **cases** component directly addresses studying people who have already developed the disease to identify **risk factors** and **exposures** that led to the condition. - This is a **retrospective study design** that works backward from disease to exposure. *Control cohort* - A control cohort refers to a group of individuals who **do not have the disease or exposure** of interest and serve as a comparison group. - This is a component of studies, not a study type itself. - This option focuses on **healthy or unexposed individuals**, not those who have already contracted the disease. *Cohort* - A **cohort study** follows a group of individuals over time to observe who develops disease (**prospective**) or examines past exposures and outcomes (**retrospective**). - While it may include diseased individuals, its primary focus is on **disease incidence** and **temporal relationships**, starting from exposure and moving forward to disease outcome. *Cross-sectional* - A **cross-sectional study** examines disease and exposure status **simultaneously** at a single point in time. - It provides a **snapshot** of prevalence but does not specifically focus on examining those who have already contracted disease to identify risk factors. - It cannot establish **temporal relationships** between exposure and disease.
Question 2: In the context of a cohort study, which of the following statistical measures is not typically used?
- A. Incidence rate
- B. Attributable risk percentage
- C. Relative risk
- D. Odds ratio (Correct Answer)
Explanation: ***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.
Question 3: Berksonian bias is a type of ?
- A. Selection bias (Correct Answer)
- B. Information bias
- C. Interviewer bias
- D. Recall bias
Explanation: ***Selection bias*** - **Berkson's bias** is a form of **selection bias** that arises in studies conducted using hospital data. - It occurs when the probability of admission to a hospital or inclusion in a study is conditional on both exposure and disease status, leading to a **flawed association** between them. *Interviewer bias* - **Interviewer bias** is a type of **information bias** where the interviewer's expectations or knowledge about the study or participants influence the way information is sought or recorded. - This typically affects the **data collection process** and not the selection of participants. *Information bias* - **Information bias** is a broad category of biases that arise from **systematic errors in measurement** or classification of exposure or disease. - While Berkson's bias can lead to misinformation, its root cause is in how subjects are selected, not how data on those subjects is collected after selection. *Recall bias* - **Recall bias** is a type of **information bias** where there are systematic differences in the way participants **recall past events or exposures**. - It is particularly common in **case-control studies** where individuals with a disease may remember exposures differently than healthy controls.
Question 4: According to Hill's criteria, which of the following is NOT a criterion for establishing causality in noncommunicable diseases?
- A. Strength of association
- B. Absence of temporal sequence (Correct Answer)
- C. Dose response relationship
- D. Specificity of association
Explanation: ***Absence of temporal sequence*** - A crucial criterion for establishing causality is the **presence of a temporal sequence**, meaning the exposure must precede the outcome. - The **absence of a temporal sequence** would argue directly against causality, as the cause cannot come after the effect. *Strength of association* - This criterion suggests that a **stronger statistical association** between an exposure and an outcome makes a causal relationship more likely. - A large **relative risk** or **odds ratio** indicates a strong association. *Dose response relationship* - This criterion implies that as the **amount or duration of exposure increases**, the **risk or severity of the outcome also increases**. - This **dose-response gradient** strengthens the argument for a causal link. *Specificity of association* - This criterion suggests that a single exposure leads to a **specific effect**, and not a wide range of unrelated effects. - While helpful, **lack of specificity does not rule out causality**, as many exposures can have multiple effects.
Question 5: 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 6: A 10-year long study concerning the use of fluorides and pit and fissure sealants in the control of caries on the same population group is an example of:
- A. Experimental study
- B. Case control study
- C. Prospective cohort study (Correct Answer)
- D. Cross sectional study
Explanation: ***Prospective cohort study*** - This study design involves following a group of individuals (**cohort**) over a period of time (10 years) to observe the development of an outcome (caries control) in relation to specific exposures (fluorides and sealants). - The study starts with individuals free of the outcome and collects data prospectively, making it ideal for studying the **incidence** and **natural history** of diseases or the effectiveness of interventions over time. *Experimental study* - An experimental study, such as a **randomized controlled trial (RCT)**, would involve the active manipulation of an intervention and random assignment of subjects to different groups (e.g., fluoride group vs. no fluoride group). - While interventions are being observed (fluorides, sealants), the description does not mention random assignment or direct researcher manipulation for comparison, only observation over time. *Case control study* - A case-control study is **retrospective**, meaning it starts with an outcome (cases with caries vs. controls without caries) and looks back in time to identify potential exposures. - This study, however, follows the same population group for 10 years to observe outcomes, which is a key characteristic of prospective designs. *Cross sectional study* - A cross-sectional study measures exposures and outcomes at a **single point in time**, providing a snapshot of the population. - This study, lasting 10 years and observing changes over time, clearly goes beyond a single time point and is designed to assess changes and relationships longitudinally.
Question 7: What is the primary purpose of interventional studies in clinical research?
- A. Confirming Hypotheses
- B. Testing Hypotheses (Correct Answer)
- C. Manipulating Hypotheses
- D. Formulating Hypotheses
Explanation: ***Testing Hypotheses*** - Interventional studies, such as **randomized controlled trials**, are specifically designed to **test cause-and-effect relationships** by actively intervening. - They aim to determine if a specific intervention (e.g., a drug, a therapy) produces a hypothesized outcome. *Confirming Hypotheses* - While interventional studies can confirm hypotheses, their primary role is not just confirmation but the initial **rigorous testing** of a hypothesis under controlled conditions. - Confirmation often implies that previous evidence already strongly supports the hypothesis. *Manipulating Hypotheses* - Hypotheses themselves are not "manipulated"; rather, the **variables** within the study design (e.g., treatment groups, dosages) are manipulated to test the hypothesis. - This option incorrectly applies the concept of manipulation to the hypothesis. *Formulating Hypotheses* - Hypothesis formulation usually occurs during the **observational research phase** or through literature review, *before* interventional studies are designed. - Observational studies or descriptive research are more typically used for generating new hypotheses.
Question 8: What is the definition of Population Attributable Risk?
- A. The difference between incidence in population and incidence in exposed.
- B. The difference between incidence in population and incidence in non-exposed. (Correct Answer)
- C. The difference between incidence in population and incidence in non-exposed compared with incidence in exposed.
- D. The difference between incidence in exposed and incidence in non-exposed.
Explanation: ***Correct: The difference between incidence in population and incidence in non-exposed.*** - **Population Attributable Risk (PAR)** quantifies the excess incidence of disease in the total population that is attributable to a specific exposure. - Formula: **PAR = Incidence in total population - Incidence in unexposed** - It represents the amount of disease burden that would be eliminated from the entire population if the exposure were completely removed. - PAR accounts for both the strength of association and the prevalence of exposure in the population. *Incorrect: The difference between incidence in population and incidence in exposed.* - This formula (I(population) - I(exposed)) does not correctly capture PAR. - This calculation does not isolate the portion of disease attributable to the exposure across the entire population. - It fails to provide meaningful information about attributable risk. *Incorrect: The difference between incidence in population and incidence in non-exposed compared with incidence in exposed.* - This option introduces unnecessary complexity and is not the standard definition of PAR. - PAR is a simple difference, not a comparative ratio involving exposed individuals. - This description confuses PAR with other epidemiological measures. *Incorrect: The difference between incidence in exposed and incidence in non-exposed.* - This describes **Attributable Risk (AR)** or **Risk Difference (RD)**, not Population Attributable Risk. - Formula: **AR = I(exposed) - I(unexposed)** - AR measures excess risk in the exposed group only, without considering the prevalence of exposure in the total population. - PAR differs from AR by accounting for how common the exposure is in the population.
Question 9: A new test was developed for detection of COVID-19. What is the sensitivity of the test as per the information provided above?
- A. 97%
- B. 37.5% (Correct Answer)
- C. 20.5%
- D. 60%
Explanation: ***37.5%*** - **Sensitivity** is calculated as the number of **true positives** divided by the sum of true positives and false negatives (i.e., total number of individuals with the disease). - From the table, **True Positives (Test Positive and Disease +)** = 60, and **False Negatives (Test Negative and Disease +)** = 100. So, sensitivity = 60 / (60 + 100) = 60 / 160 = 0.375 or 37.5%. *97%* - This value is incorrect. It might be confused with **Negative Predictive Value (NPV)**, which is the probability that subjects with a negative test truly don't have the disease (1800/1900 ≈ 0.947 or 94.7%), but it's not 97%. - It does not correctly represent the calculation for sensitivity as described above. *20.5%* - This value is incorrect. It does not correspond to any standard epidemiological measure of test performance based on the provided data. - This percentage might arise from an incorrect division or addition of values from the table. *60%* - This value is incorrect. While 60 **true positives** are present, sensitivity requires dividing this by the total number of diseased individuals, not just any other total. - This could be confused with the ratio of true positives to total positive tests (Positive Predictive Value), which would be 60/100, resulting in 60%, but this is not sensitivity.
Question 10: Which of the following Screening methods for Disease is the least useful?
- A. Selective screening
- B. High risk group screening
- C. Mass screening (Correct Answer)
- D. Multiphasic screening
Explanation: ***Mass screening*** - Mass screening is the **least useful** screening method when applied indiscriminately to entire unselected populations, particularly for diseases with **low prevalence**. - This approach tests everyone regardless of risk factors, making it highly **resource-intensive** with low efficiency and poor **positive predictive value** for rare conditions. - The high rate of **false positives** leads to unnecessary follow-up investigations, patient anxiety, and wastage of healthcare resources, making it the least cost-effective screening strategy. *Selective screening* - **Selective screening** targets specific high-risk groups or individuals with certain exposures, significantly improving the **yield** and **cost-effectiveness** of the screening program. - This approach focuses resources where the **prevalence of disease** is higher, increasing the likelihood of detecting true cases and reducing false positives compared to mass screening. *High risk group screening* - **High-risk group screening** focuses on individuals with known risk factors, family history, or exposures that significantly increase their likelihood of developing a disease. - This method is highly effective for diseases with clear risk profiles, as it maximizes the **positive predictive value** of the screening test and optimizes resource allocation. *Multiphasic screening* - **Multiphasic screening** involves the simultaneous application of multiple screening tests to detect several conditions at once during a single healthcare encounter. - This approach can be efficient for detecting multiple prevalent diseases in certain populations, offering comprehensive health assessment while being more useful than mass screening due to its targeted nature.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free