Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1761: Which of the following is considered the weakest criterion in the causal relationship hypothesis?

A. Temporal relationship (cause precedes effect)
B. Specificity of association (one-to-one relationship) (Correct Answer)
C. Biological gradient (increased exposure leads to increased effect)
D. Strength of association (stronger relationships are more reliable)

Explanation: ***Specificity of association (one-to-one relationship)*** - While a specific, one-to-one relationship between cause and effect (e.g., one exposure leading to only one disease) **might seem intuitive**, it is often not observed in complex biological systems. - Many diseases have **multiple causes** (e.g., lung cancer can be caused by smoking, asbestos, radon), and many exposures can lead to **multiple effects** (e.g., smoking causes lung cancer, heart disease, COPD). Therefore, requiring specificity as a strong criterion significantly limits its applicability and validity in establishing causality. *Temporal relationship (cause precedes effect)* - This is a **necessary criterion** for causality, meaning the cause must always occur before the effect. - Without a correct temporal sequence, it is **impossible to establish a causal link**, as an effect cannot precede its cause. *Biological gradient (increased exposure leads to increased effect)* - A **dose-response relationship** suggests that as the exposure level increases, the risk or severity of the outcome also increases. - This criterion provides strong evidence for causality because it indicates a **direct biological mechanism** linking the exposure to the effect. *Strength of association (stronger relationships are more reliable)* - A **strong statistical association** (e.g., a high relative risk or odds ratio) makes it less likely that the observed relationship is due to confounding factors. - While not solely sufficient, a strong association is a **powerful indicator** that a causal link may exist.

Question 1762: How often is the Sample Registration System conducted in India?

A. 2 years
B. 5 years
C. 6 months
D. 1 year (Correct Answer)

Explanation: ***1 year*** - The **Sample Registration System (SRS)** in India is a large-scale demographic survey conducted **annually** to provide reliable estimates of birth rates, death rates, and other fertility and mortality indicators. - Its annual nature allows for regular monitoring of demographic changes and health trends across different states and regions. *6 months* - While some surveys or data collections might occur semi-annually, the comprehensive SRS is not conducted every six months. - Conducting a system as extensive as the SRS twice a year would be logistically challenging and resource-intensive. *2 years* - A biennial (every two years) frequency would mean less up-to-date data for tracking rapid demographic shifts or evaluating the immediate impact of health interventions. - The need for current statistics on vital events necessitates a more frequent survey than every two years. *5 years* - A quinquennial (every five years) frequency would provide very infrequent data, which is insufficient for effective public health planning and policy formulation. - Key demographic indicators are needed more regularly than every five years to respond to evolving health and population needs.

Question 1763: What is exponential growth in the context of population dynamics?

A. Gradual increase in population size.
B. Population growth that is restricted by environmental factors.
C. No significant change in population size.
D. Rapid increase in population size where growth rate is proportional to current population. (Correct Answer)

Explanation: ***Rapid increase in population size where growth rate is proportional to current population.*** - **Exponential growth** occurs when a population increases at a **constant rate proportional to its size**, resulting in accelerating absolute numbers over time. - This produces a characteristic **J-shaped curve** where the population grows slowly at first, then increasingly rapidly. - Mathematically expressed as N(t) = N₀e^(rt), where birth rate consistently exceeds death rate. - Occurs in **ideal conditions** with abundant resources and minimal limiting factors. *Gradual increase in population size.* - A gradual increase implies **linear growth** with a constant absolute increment per time period, not the accelerating pattern of exponential growth. - While exponential growth may appear gradual initially, its defining feature is the **increasing rate of growth** over time. *Population growth that is restricted by environmental factors.* - This describes **logistic growth** (S-shaped curve), where environmental resistance slows growth as the population approaches carrying capacity. - Exponential growth, in contrast, assumes **no significant environmental limitations** on resources or space. *No significant change in population size.* - This represents a **stable or stationary population** where birth and death rates are balanced. - The opposite of exponential growth, which shows **rapid and accelerating increase** in population numbers.

Question 1764: Which of the following is NOT one of Bradford Hill's criteria for causation?

A. Consistency of association
B. Specificity of association
C. Strength of association
D. Absence of temporal relationship (Correct Answer)

Explanation: ***Absence of temporal relationship*** - Bradford Hill's criteria include **temporality** (temporal relationship), which states that the cause must precede the effect in time. - The criterion is the **presence** of a temporal relationship, not its absence. - "Absence of temporal relationship" is therefore NOT one of Bradford Hill's criteria—it is the opposite of what the criterion requires. - This is the correct answer to this "NOT" question. *Strength of association* - This **IS** one of Bradford Hill's criteria. - It refers to the **magnitude of the association** between exposure and outcome (measured by relative risk, odds ratio, etc.). - A stronger association provides more evidence for causality. *Consistency of association* - This **IS** one of Bradford Hill's criteria. - It means the association is observed **repeatedly** across different studies, populations, settings, and times. - Consistent replication strengthens the causal argument. *Specificity of association* - This **IS** one of Bradford Hill's criteria. - It suggests that a specific exposure leads to a specific outcome with limited alternative explanations. - While supportive of causation, Hill noted this criterion is less essential as many exposures have multiple effects.

Question 1765: Most commonly used blinding technique in epidemiological studies?

A. None of the options
B. Single blinding
C. Double blinding (Correct Answer)
D. Triple blinding

Explanation: ***Double blinding*** - In **double blinding**, neither the **participants** nor the **researchers** administering the intervention and collecting data know who is in the treatment group versus the control group. - This method is widely used to prevent **observer bias** from the researchers and **participant bias** (e.g., placebo effect) from the subjects, thereby strengthening the study's internal validity. *Single blinding* - In **single blinding**, only the **participants** are unaware of their assignment to either the treatment or control group. - While it helps reduce participant bias, the **researchers' knowledge** of group assignments can still introduce **observer bias**, making it less rigorous than double blinding. *Triple blinding* - **Triple blinding** extends double blinding by ensuring that the **data analysts** are also unaware of the participant group assignments. - This technique further minimizes bias in the **interpretation and analysis of results**, but it is less commonly implemented due to its complexity and increased logistical challenges compared to double blinding. *None of the options* - This option is incorrect because **blinding techniques** are fundamental tools in epidemiological studies and clinical trials to ensure the objectivity and reliability of research findings. - **Blinding** helps eliminate conscious and unconscious biases that could otherwise influence study outcomes.

Question 1766: Which of the following statements is true regarding a combined prospective-retrospective study?

A. Only prospective follow-up from current time point
B. Retrospective identification of cohort followed by prospective follow-up (Correct Answer)
C. Cross-sectional assessment at a single time point
D. Only retrospective data collection from past records

Explanation: ***Retrospective identification of cohort followed by prospective follow-up*** - This correctly describes a **combined prospective-retrospective study** (also called an **ambispective or historical prospective study**) - The study begins by **retrospectively identifying a cohort** from past records (e.g., employees exposed to a chemical 10 years ago) - **Past exposure data is collected retrospectively** from existing records - The identified cohort is then **followed forward prospectively** from the current time point to observe future outcomes - This approach combines the **efficiency of retrospective data collection** with the **rigor of prospective follow-up** *Only prospective follow-up from current time point* - The word **"only"** is the critical error - it excludes the retrospective component - This describes a **purely prospective cohort study**, not a combined study - A combined study must include **both retrospective and prospective elements** *Only retrospective data collection from past records* - This describes a **purely retrospective study** (case-control or retrospective cohort) - It lacks the prospective follow-up component essential to a combined study *Cross-sectional assessment at a single time point* - This defines a **cross-sectional study** that provides a snapshot at one moment - It involves neither retrospective cohort identification nor prospective follow-up

Question 1767: Which study design is most effective for investigating rare adverse effects of a drug?

A. Cohort study
B. Cross-sectional study
C. Case-control study (Correct Answer)
D. Clinical trial/experimental study

Explanation: ***Case-control study*** - This design starts by identifying individuals with the **rare adverse effect (cases)** and a control group without the effect to look back for exposure to the drug. - It is efficient for studying rare outcomes because it doesn't require following a large population for a long time to observe few events. *Cohort study* - A **cohort study** follows a group of individuals exposed and unexposed to a drug forward in time to observe outcomes. - While good for common outcomes, it would require an **extremely large sample size** and a long follow-up period to observe rare adverse drug effects. *Cross-sectional study* - A **cross-sectional study** assesses exposure and outcome simultaneously at a single point in time. - This design is suitable for determining **prevalence** but cannot establish temporal relationships between drug exposure and rare adverse effects, nor is it efficient for rare outcomes. *Clinical trial/experimental study* - **Clinical trials** are primarily designed to test the efficacy and safety of new interventions, usually focusing on common adverse effects. - They are generally **not powered** or long enough to detect rare adverse events, as such events would occur in very few participants, if any.

Question 1768: Bladder cancer can occur in those who are working in dye industry for 25 years. Which study design is most appropriate for establishing a causal relationship between dye industry work and bladder cancer?

A. Cross-sectional study
B. Case-control study
C. Cohort study (Correct Answer)
D. Randomized control trial

Explanation: ***Cohort study*** - A **cohort study** tracks a group of individuals exposed to a risk factor (dye industry work) and a group not exposed over time to see who develops the outcome (bladder cancer). - This design allows for the calculation of **incidence rates** and relative risk, which are crucial for establishing a causal link, especially when the exposure is rare or specific. - Cohort studies establish **temporal relationship** (exposure precedes disease) and can demonstrate a **dose-response relationship**, both essential for proving causality. *Cross-sectional study* - A **cross-sectional study** assesses exposure and outcome simultaneously at a single point in time, making it difficult to determine the temporal sequence of events. - While it can identify associations, it cannot definitively establish a **cause-and-effect relationship** because it doesn't observe outcomes developing over time. *Case-control study* - A **case-control study** compares individuals with the outcome (cases) to individuals without the outcome (controls) and retrospectively looks for differences in past exposures. - While useful for studying **rare diseases** and can suggest associations, it is prone to **recall bias** regarding exposure history and cannot establish causality as definitively as cohort studies. *Randomized control trial* - A **randomized controlled trial (RCT)** involves randomly assigning participants to an intervention group or a control group and following them prospectively. - While RCTs provide the strongest evidence for causality, it would be **unethical** to intentionally expose people to a known carcinogen like dye industry chemicals for research purposes.

Question 1769: Which of the following is an example of a case-control study?

A. Framingham heart study
B. PVC exposure and angiosarcoma of the liver (Correct Answer)
C. Doll & Hill Study
D. Thalidomide exposure and its association with teratogenicity

Explanation: ***PVC exposure and angiosarcoma of the liver*** - This is a classic example of a **case-control study** where individuals with a rare disease (angiosarcoma of the liver) are identified (cases) and compared to a control group without the disease to determine past exposures (PVC). - The study looked back in time to identify differences in exposure between cases and controls. *Framingham heart study (cohort study)* - The Framingham Heart Study is a well-known **prospective cohort study** that has followed participants over time to observe the development of cardiovascular disease. - In a cohort study, researchers identify a group of individuals and follow them forward in time to see who develops the outcome of interest, making it different from a case-control design. *Doll & Hill Study (cohort study)* - The Doll & Hill study is a landmark **cohort study** that investigated the association between smoking and lung cancer by following a group of British doctors over several years. - This study started with healthy individuals and observed them over time to see who developed lung cancer, which is characteristic of a cohort design. *Thalidomide exposure and its association with teratogenicity* - While the thalidomide tragedy led to crucial epidemiological investigations, the initial identification of the association was often through **case series** or **descriptive epidemiology**, noting an unusual clustering of rare birth defects among infants whose mothers took thalidomide. - Subsequent studies might have incorporated case-control elements, but the prompt asks for an example of a case-control study, and this event itself is generally cited for its role in pharmacovigilance and observational studies rather than a single, classic case-control study example in the way "PVC and angiosarcoma" is.

Question 1770: Which of the following is the primary component of the AFP (Acute Flaccid Paralysis) case definition used in polio surveillance?

A. All of the above
B. Stool specimen positive for poliovirus
C. Onset of acute flaccid paralysis (Correct Answer)
D. Presence of residual paralysis after 60 days

Explanation: ***Onset of acute flaccid paralysis*** - The primary component of the **AFP case definition** for polio surveillance is the acute onset of **flaccid paralysis** in a child under 15 years, or paralytic illness in a person of any age when polio is suspected. - This definition is crucial for identifying all potential cases of polio, regardless of the cause, to ensure thorough investigation and prevent outbreaks. *Stool specimen positive for poliovirus* - A positive stool specimen for poliovirus is a **laboratory confirmation** of polio infection, but it is not the primary component of the initial case definition. - The AFP case definition aims for **high sensitivity** to capture all possible cases for investigation, even before laboratory results are available. *Presence of residual paralysis after 60 days* - Residual paralysis after 60 days is an important indicator for **classifying a confirmed polio case** and understanding the long-term impact. - However, it is a **follow-up criterion** used after the initial detection of AFP, not the primary component that triggers the initial surveillance. *All of the above* - While laboratory confirmation and residual paralysis provide further information about a case, the **initial identification relies specifically on the clinical presentation** of acute flaccid paralysis. - The broad clinical definition ensures that no potential polio case is missed, initiating an immediate public health response.

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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