Experimental Epidemiology — MCQs

10 questions

Which of the following is not considered a type of subject bias?

In which phase of clinical trials is drug dosing typically determined?

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

In which type of study is selection bias most likely to occur?

The best indicator for a potential explosiveness of plague outbreak is:

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?

A rheumatologist is interested in studying the association between osteoporosis and the risk of sustaining a distal radius fracture. To explore this association, she develops a retrospective study design in which she identifies patients in a large institutional database over the age of 55 with and without osteoporosis, then follows them over a 10-year period to identify cases of distal radius fracture. She matches patients on age, sex, and body mass index to control for known confounding. After completing the study, she finds that patients with osteoporosis were at an increased risk of developing distal radius fractures. Which of the following study designs did this investigator use in this case?

Q10

A researcher is investigating whether there is an association between the use of social media in teenagers and bipolar disorder. In order to study this potential relationship, she collects data from people who have bipolar disorder and matched controls without the disorder. She then asks how much on average these individuals used social media in the 3 years prior to their diagnosis. This continuous data is divided into 2 groups: those who used more than 2 hours per day and those who used less than 2 hours per day. She finds that out of 1000 subjects, 500 had bipolar disorder of which 300 used social media more than 2 hours per day. She also finds that 400 subjects who did not have the disorder also did not use social media more than 2 hours per day. Which of the following is the odds ratio for development of bipolar disorder after being exposed to more social media?

Experimental Epidemiology Indian Medical PG Practice Questions and MCQs

Question 1: Which of the following is not considered a type of subject bias?

A. Recall bias
B. Selection bias (Correct Answer)
C. Hawthorne bias
D. Reporting bias

Explanation: ***Selection bias*** - **Selection bias** occurs when participants are chosen or remain in a study in a way that introduces a systematic error, leading to a sample that does not accurately represent the target population. - It is a **study design and sampling issue** that occurs at the **recruitment** or **retention stage**, not a bias arising from the subjects' own behavior or reporting. - Unlike subject biases, selection bias is introduced by the **investigators or study methodology**, not by the participants themselves. *Recall bias* - **Recall bias** is a type of **subject bias** where participants differentially remember and report past exposures based on their outcome status. - Subjects with disease may recall exposures more accurately than healthy controls, introducing **systematic error from the subject's memory**. *Hawthorne bias* - **Hawthorne bias** (observer effect) is a **subject bias** where participants modify their behavior because they know they are being studied. - The **subject's awareness** of observation directly influences their actions, responses, or adherence. *Reporting bias* - **Reporting bias** is a **subject bias** where participants selectively disclose or withhold information based on social desirability, embarrassment, or perceived consequences. - This bias arises from the **subject's decision** about what to report.

Question 2: Match the following columns on Epidemiology Guidelines: | A. CARE | 1. RCT | | :-- | :-- | | B. CONSORT | 2. Case report | | C. PRISMA | 3. Observational study | | D. STROBE/MOOSE | 4. Systematic Review |

A. A2-B1-C4-D3 (Correct Answer)
B. A2-B4-C1-D3
C. A4-B1-C3-D2
D. A4-B1-C2-D3

Explanation: ***A2-B1-C4-D3*** - **CARE Guidelines** provide essential reporting standards for **case reports** and case series to enhance their value and transparency. - **CONSORT (Consolidated Standards of Reporting Trials)** is specifically designed for the reporting of **Randomized Controlled Trials (RCTs)**. - **PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses)** provides a minimum set of items for reporting in **systematic reviews** and meta-analyses. - **STROBE (STrengthening the Reporting of OBservational studies in Epidemiology)** and **MOOSE (Meta-analysis Of Observational Studies in Epidemiology)** are reporting guidelines for **observational studies**, including cohort, case-control, and cross-sectional studies. *A2-B4-C1-D3* - Incorrectly pairs CONSORT with systematic reviews (should be RCTs) and PRISMA with RCTs (should be systematic reviews). - CONSORT is the gold standard for **reporting RCTs**, while PRISMA is designed for **systematic reviews and meta-analyses**. *A4-B1-C3-D2* - Incorrectly matches CARE with systematic reviews, PRISMA with observational studies, and STROBE/MOOSE with case reports. - CARE is specifically for **case reports and case series**, PRISMA for **systematic reviews**, and STROBE/MOOSE for **observational epidemiological studies**. *A4-B1-C2-D3* - Incorrectly pairs CARE with systematic reviews and PRISMA with case reports. - This reverses the actual purpose: CARE is designed for **case reports**, while PRISMA guides **systematic reviews and meta-analyses**.

Question 3: In which phase of clinical trials is drug dosing typically determined?

A. Phase 1 (Correct Answer)
B. Phase 2
C. Phase 3
D. Phase 4
E. Phase 0

Explanation: ***Phase 1*** - This phase involves a small group of **healthy volunteers** to assess the drug's safety, **pharmacokinetics (PK)**, and establish an initial dosing range. - The primary goal is to determine a **safe dosage level**, establish the **maximum tolerated dose (MTD)**, and identify potential side effects. - This is where drug dosing is **typically determined**. *Phase 0* - This is an exploratory phase involving **microdosing** studies with subtherapeutic doses. - The goal is to gather preliminary PK/PD data, but **not to determine therapeutic dosing**. *Phase 2* - This phase involves a larger group of **patients** with the condition to be treated. - The main goal is to evaluate the drug's **effectiveness** and further assess safety, but not primarily to determine initial dosing. *Phase 3* - This phase involves a large number of patients across multiple sites to confirm the drug's **efficacy** and monitor side effects in a broader population. - Dosing strategies have generally been established in earlier phases, and this phase primarily validates them. *Phase 4* - This phase occurs **after a drug has been approved** and marketed. - It involves ongoing surveillance to monitor long-term effects, collect additional information on safety, and identify new uses, but not initial dose determination.

Question 4: What is a key benefit of Randomized Controlled Trials (RCTs) in clinical research?

A. They can be conducted more quickly than other study types.
B. They minimize selection bias. (Correct Answer)
C. They are ideal for studying rare diseases.
D. They are generally less expensive than other study types.

Explanation: ***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**.

Question 5: In which type of study is selection bias most likely to occur?

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

Explanation: ***Case-control study*** - **Selection bias** is a common concern as cases and controls are often selected based on their disease status, making it difficult to ensure they represent the underlying population's exposure distribution. - This study design inherently involves **retrospective data collection**, increasing the risk of differential selection of participants based on their exposure history. - The retrospective nature and non-random selection of cases and controls makes this study type **most vulnerable** to selection bias. *Cohort study* - While selection bias can occur (e.g., participants lost to follow-up), it is generally **less pronounced** than in case-control studies because subjects are selected based on **exposure status** before disease development, minimizing bias related to outcome. - The prospective nature of many cohort studies reduces the risk of selecting participants based on a known outcome. *Cross-sectional study* - Selection bias can occur if the sample is not representative of the target population. - However, since both exposure and outcome are measured **simultaneously**, there is no temporal selection based on outcome status as seen in case-control studies. - The risk is lower than case-control studies as participants are typically selected from a defined population at one point in time. *Randomized controlled trial (RCT)* - **Randomization** is specifically designed to minimize selection bias by ensuring that exposure (intervention) assignment is independent of participant characteristics. - The process of randomly assigning participants to treatment or control groups reduces the likelihood of systemic differences between groups at baseline.

Question 6: The best indicator for a potential explosiveness of plague outbreak is:

A. Burrow index
B. Cheopis index (Correct Answer)
C. Specific percentage of fleas
D. Total flea index

Explanation: ***Cheopis index*** - The **Cheopis index** (average number of *Xenopsylla cheopis* fleas per rodent) is the **best indicator for explosive plague outbreaks**. - *X. cheopis* (oriental rat flea) is the **primary vector** of *Yersinia pestis* and most efficient at transmission. - When the Cheopis index **exceeds 1.0**, it indicates critical conditions for rapid epidemic spread and explosive outbreak potential. - This index specifically measures the most dangerous vector species, making it the most precise predictor of outbreak explosiveness. *Total flea index* - Measures the average number of **all flea species** per rodent, regardless of vector competence. - While useful for general surveillance, it **lacks specificity** as it includes non-vector or less efficient vector species. - Does not specifically predict explosiveness as effectively as focusing on the primary vector species. *Burrow index* - Reflects rodent population density and activity (number of active burrows per hectare). - Indicates **host availability** but not the immediate transmission risk from vectors. - Important for understanding epizootic conditions but indirect measure of outbreak potential. *Specific percentage of fleas* - This term is **vague and non-standard** in plague epidemiology terminology. - Could refer to various metrics (percentage infected, percentage of specific species) without clear definition. - Not a recognized standardized indicator for plague surveillance.

Question 7: 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 8: 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.

Question 9: A rheumatologist is interested in studying the association between osteoporosis and the risk of sustaining a distal radius fracture. To explore this association, she develops a retrospective study design in which she identifies patients in a large institutional database over the age of 55 with and without osteoporosis, then follows them over a 10-year period to identify cases of distal radius fracture. She matches patients on age, sex, and body mass index to control for known confounding. After completing the study, she finds that patients with osteoporosis were at an increased risk of developing distal radius fractures. Which of the following study designs did this investigator use in this case?

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

Explanation: ***Cohort study*** - This study design **identifies groups based on exposure status** (with or without osteoporosis) and **follows them forward in time** to observe the development of an outcome (distal radius fracture). - The investigator collected data on exposure first, then observed outcomes over a 10-year period, which is characteristic of a **prospective** or **retrospective cohort study**. *Case-control study* - This design **starts with identifying individuals with the outcome (cases)** and a comparison group without the outcome (controls), then **looks backward in time** to determine past exposures. - The study described here starts with exposure status (osteoporosis) first, not the outcome (fracture). *Cross-sectional study* - This study assesses **exposure and outcome simultaneously at a single point in time**, providing a "snapshot" of the prevalence of both. - The rheumatologist in this scenario followed patients over a 10-year period, indicating a longitudinal design, not a single point in time. *Ecological study* - This type of study **analyzes data at a population level**, rather than at the individual level, to find correlations between exposure and outcome. - The study described explicitly involves identifying and following **individual patients**, not groups or populations.

Question 10: A researcher is investigating whether there is an association between the use of social media in teenagers and bipolar disorder. In order to study this potential relationship, she collects data from people who have bipolar disorder and matched controls without the disorder. She then asks how much on average these individuals used social media in the 3 years prior to their diagnosis. This continuous data is divided into 2 groups: those who used more than 2 hours per day and those who used less than 2 hours per day. She finds that out of 1000 subjects, 500 had bipolar disorder of which 300 used social media more than 2 hours per day. She also finds that 400 subjects who did not have the disorder also did not use social media more than 2 hours per day. Which of the following is the odds ratio for development of bipolar disorder after being exposed to more social media?

A. 1.5
B. 6 (Correct Answer)
C. 0.17
D. 0.67

Explanation: ***6*** - To calculate the odds ratio, we first construct a 2x2 table [1]: - Bipolar Disorder (Cases): 500 - No Bipolar Disorder (Controls): 500 (1000 total subjects - 500 cases) - Cases exposed to more social media (>2 hrs/day): 300 - Cases not exposed to more social media (≤2 hrs/day): 200 (500 - 300) - Controls not exposed to more social media (≤2 hrs/day): 400 - Controls exposed to more social media (>2 hrs/day): 100 (500 - 400) - The odds ratio (OR) is calculated as (odds of exposure in cases) / (odds of exposure in controls) = (300/200) / (100/400) = 1.5 / 0.25 = **6** [1]. *1.5* - This value represents the **odds of exposure** (more than 2 hours of social media) in individuals with bipolar disorder (300 cases exposed / 200 cases unexposed = 1.5). - It is not the odds ratio, which compares these odds to the odds of exposure in the control group. *0.17* - This value is close to the reciprocal of 6 (1/6 ≈ 0.166), suggesting a potential miscalculation or an inverted odds ratio. - An odds ratio of 0.17 would imply a protective effect (lower odds of bipolar disorder with more social media), which is contrary to the calculation and typical interpretation in this context. *0.67* - This value is the reciprocal of 1.5 (1/1.5 ≈ 0.67) which represents the odds of *not* being exposed in cases (200/300). - It does not represent the correct odds ratio, which compares the odds of exposure in cases to the odds of exposure in controls.

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