Epidemiology Practice Questions

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

Absence of temporal relationship. ***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.

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

Case-control study. ***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.

Q: 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?

Cohort study. ***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.

Q: What is a key benefit of Randomized Controlled Trials (RCTs) in clinical research?

They minimize selection bias.. ***They minimize selection bias.*** - **Randomization** in RCTs ensures that participants have an equal chance of being assigned to any of the treatment groups, thereby balancing potential **confounding factors** across groups. - This balance helps to ensure that any observed differences in outcomes between groups are more likely due to the intervention being studied rather than pre-existing differences among participants, thus minimizing **selection bias**. *They can be conducted more quickly than other study types.* - RCTs often require **extensive planning**, recruitment, and follow-up periods, making them one of the **most time-consuming** study designs. - The need for sufficient **power** to detect meaningful differences often translates into longer study durations. *They are ideal for studying rare diseases.* - Due to the requirement for **large sample sizes** to demonstrate statistical significance, RCTs are **not practical** for diseases with low prevalence. - Recruiting enough participants with a rare disease for an RCT can be extremely challenging and often **unfeasible**. *They are generally less expensive than other study types.* - RCTs are typically among the **most expensive** study designs because they involve extensive participant recruitment, intervention administration, data collection, and long-term follow-up. - The costs associated with staff, resources, and monitoring for ethical compliance contribute to their **high financial burden**.

Q: What is the most important criterion in a causal relationship hypothesis?

Temporal association. ***Temporal association*** - This is the **sine qua non** of causality, meaning the exposure or cause must always precede the outcome or effect in time. - Without the exposure occurring before the disease, a causal link cannot be established, even if other criteria are met. *Coherence of association* - This refers to the consistency of findings with current scientific knowledge and **biological plausibility**. - While important for supporting causality, a coherent explanation is not sufficient in itself to prove causation and may even be misleading if current knowledge is incomplete. *Specificity of association* - This criterion suggests that a single exposure should lead to a single outcome, or a single outcome should be caused by a single exposure. - However, many diseases have **multiple causes**, and many exposures can lead to multiple effects, making this a weak criterion in modern epidemiology. *Strength of association* - A **strong association**, often measured by a high relative risk or odds ratio, makes a causal relationship more likely but does not guarantee it. - Strong associations can still be due to **confounding factors** or bias, and weak associations can be causal.

Q: Spot map is used for?

Local distribution of disease. ***Local distribution of disease*** - A **spot map** visually represents the geographic distribution of individual cases of a disease or health event. - Each 'spot' on the map corresponds to the exact location where a case occurred, making it ideal for identifying **clusters** or patterns of disease within a specific area. *Rural-urban variation* - While a spot map could potentially show cases in both rural and urban settings, its primary purpose is not to specifically highlight the differences between these two broad categories. - Other types of **thematic maps** or **statistical analyses** are better suited for assessing rural-urban variations. *National variation* - A spot map would be impractical for showing national variation in detail, as it would require plotting individual cases across an entire country, leading to an overly cluttered and uninterpretable image. - **Choropleth maps**, which use shading or colors to represent data for predefined geographic areas (like states or provinces), are more appropriate for illustrating national trends or variations. *None of the options* - This option is incorrect because the primary use of a spot map aligns directly with illustrating the **local distribution of disease**.

Question 1

What is exponential growth in the context of population dynamics?

Accepted Answer

Rapid increase in population size where growth rate is proportional to current population.

Answer

Gradual increase in population size.

Answer

Population growth that is restricted by environmental factors.

Answer

No significant change in population size.

Question 2

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

Accepted Answer

Retrospective identification of cohort followed by prospective follow-up

Answer

Only prospective follow-up from current time point

Answer

Cross-sectional assessment at a single time point

Answer

Only retrospective data collection from past records

Question 3

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

Accepted Answer

Absence of temporal relationship

Answer

Consistency of association

Answer

Specificity of association

Answer

Strength of association

Question 4

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

Accepted Answer

Case-control study

Answer

Cohort study

Answer

Cross-sectional study

Answer

Clinical trial/experimental study

Question 5

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?

Accepted Answer

Cohort study

Answer

Cross-sectional study

Answer

Case-control study

Answer

Randomized control trial

Question 6

Multiphasic screening means-

Accepted Answer

Application of two or more screening tests in combination at one time

Answer

Application of two or more screening tests in combination at different geographical areas

Answer

Application of separate screening tests for different diseases

Answer

Application of two or more screening tests in combination at different times

Question 7

What is a key benefit of Randomized Controlled Trials (RCTs) in clinical research?

Accepted Answer

They minimize selection bias.

Answer

They can be conducted more quickly than other study types.

Answer

They are ideal for studying rare diseases.

Answer

They are generally less expensive than other study types.

Question 8

What is the definition of Population Attributable Risk?

Accepted Answer

The difference between incidence in population and incidence in non-exposed.

Answer

The difference between incidence in population and incidence in exposed.

Answer

The difference between incidence in population and incidence in non-exposed compared with incidence in exposed.

Answer

The difference between incidence in exposed and incidence in non-exposed.

Question 9

What is the most important criterion in a causal relationship hypothesis?

Accepted Answer

Temporal association

Answer

Coherence of association

Answer

Specificity of association

Answer

Strength of association

Question 10

Spot map is used for?

Accepted Answer

Local distribution of disease

Answer

Rural-urban variation

Answer

National variation

Answer

None of the options

Epidemiology — MCQs

Epidemiology — MCQs

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