Epidemiology Practice Questions

Q: Randomization is useful to eliminate which of the following?

Confounding factors. **Explanation:** **Why Confounding Factors is Correct:** Randomization is the "heart" of a Randomized Controlled Trial (RCT). Its primary purpose is to ensure that both known and unknown **confounding factors** are distributed equally between the study and control groups. By allocating participants purely by chance, randomization eliminates **selection bias** and balances prognostic factors, ensuring that any observed difference in outcome is due to the intervention alone and not an extraneous variable. It is the only method that can control for **unknown confounders**. **Why Other Options are Incorrect:** * **A & C (Observer and Patient Bias):** These are types of information/measurement bias. Randomization does not prevent these; they are eliminated through **Blinding** (Masking). Blinding ensures that neither the patient nor the researcher knows who is receiving the treatment, thus preventing subjective prejudice. * **D (Sampling Bias):** This occurs when the study population is not representative of the target population. It is eliminated through **Random Sampling** (e.g., simple random sampling), not Randomization (Random Allocation). **High-Yield Clinical Pearls for NEET-PG:** * **Randomization** = Eliminates Confounding + Selection Bias. * **Blinding** = Eliminates Observer + Patient (Information) Bias. * **Matching** = A technique used in Case-Control studies to eliminate known confounders (but cannot control for unknown ones). * **The "Gold Standard"** for testing a new drug is the Double-Blind Randomized Controlled Trial. * **Confounding by Indication:** A specific type of bias where the factor that dictates the treatment choice is also related to the outcome.

Q: Under AFP Surveillance, what is the follow-up examination period for residual paralysis?

60 days from onset of paralysis. ### Explanation **1. Why Option C is Correct:** Under the Global Polio Eradication Initiative and the National Polio Surveillance Project (NPSP), the standard protocol for **Acute Flaccid Paralysis (AFP) Surveillance** requires a follow-up clinical examination **60 days after the onset of paralysis**. The underlying medical concept is to differentiate between transient paralysis and **Residual Paralysis**. In cases of Wild Poliovirus infection, the motor neuron damage is often permanent, leading to residual weakness that persists beyond 60 days. If the paralysis has resolved by this time, the case is less likely to be Polio and more likely to be a condition like Guillain-Barré Syndrome (GBS) or transverse myelitis. **2. Why Other Options are Incorrect:** * **Option A (15 days):** This is irrelevant to residual paralysis. However, **"Adequate Stool Samples"** must be collected within 14 days of the onset of paralysis. * **Option B (33 days):** This is a distractor with no significance in the AFP surveillance timeline. * **Option D (90 days):** While some neurological recovery can continue for months, the 60-day mark is the internationally standardized "gold standard" for classifying a case as having residual paralysis for surveillance reporting. **3. High-Yield Clinical Pearls for NEET-PG:** * **Case Definition of AFP:** Any child <15 years with sudden onset of flaccid paralysis, or a person of any age if Polio is suspected. * **Stool Collection:** Two samples, 24 hours apart, within 14 days of onset ("Adequate samples"). * **Virological Classification:** A case is confirmed as Polio only if Wild Poliovirus (WPV) or Vaccine-Derived Poliovirus (VDPV) is isolated from stool. * **Non-Polio AFP Rate:** A key indicator of surveillance quality; it should be at least **2 per 100,000** children <15 years.

Q: What is the most common cancer affecting both males and females worldwide?

Lung cancer. **Explanation:** The correct answer is **Lung Cancer**. According to the latest **GLOBOCAN** data (published by the WHO/IARC), lung cancer remains the most frequently diagnosed cancer and the leading cause of cancer-related mortality globally when considering both sexes combined. **Why Lung Cancer is Correct:** Lung cancer accounts for approximately 12.4% of all new cancer cases worldwide. While Breast cancer has recently surpassed Lung cancer as the most common cancer in *females*, when the data for **both males and females are aggregated**, Lung cancer retains the top position due to its high prevalence in men and rising incidence in women. **Analysis of Incorrect Options:** * **A. Cancer of the Pancreas:** While highly lethal with a poor prognosis, it does not rank among the top five most common cancers globally. * **B. Buccal Mucosa Cancer:** This is a subset of Oral Cancer. While it is highly prevalent in specific regions like **India** (due to tobacco and betel nut chewing), it is not the most common cancer on a global scale. * **D. Colo-rectal Cancer:** This is currently the third most common cancer worldwide. While its incidence is rising due to Westernized diets and sedentary lifestyles, it still trails behind Lung and Breast cancer. **High-Yield Clinical Pearls for NEET-PG:** * **Global (Both Sexes):** Most common = Lung Cancer; Leading cause of death = Lung Cancer. * **Global (Females):** Most common = Breast Cancer. * **India (Both Sexes):** Most common = Breast Cancer (followed by Lip/Oral cavity). * **India (Males):** Most common = Lip and Oral Cavity cancer. * **India (Females):** Most common = Breast Cancer (followed by Cervical cancer). * **Screening:** Low-dose CT (LDCT) is the recommended screening tool for high-risk smokers for lung cancer.

Q: Which of the following is NOT evaluated by a cohort study?

Odds ratio. **Explanation** In epidemiology, the choice of study design dictates which measures of association can be calculated. A **Cohort Study** is a longitudinal, prospective study that starts with a group of exposed and non-exposed individuals and follows them over time to observe the development of an outcome. **Why Odds Ratio is the Correct Answer:** The **Odds Ratio (OR)** is the primary measure of association used in **Case-Control studies**. It estimates the odds of exposure among cases compared to controls. While OR can be calculated in a cohort study, it is not the standard or intended evaluation metric because cohort studies allow for the direct calculation of risk. **Analysis of Incorrect Options:** * **A. Incidence:** Cohort studies are the only observational design that can directly calculate incidence (the number of new cases in a population at risk) because they follow subjects from a healthy state to the onset of disease. * **B. Attributable Risk (AR):** AR measures the impact of an exposure (Incidence in exposed – Incidence in non-exposed). Since cohort studies provide incidence, AR can be easily derived. * **C. Relative Risk (RR):** Also known as Risk Ratio, this is the hallmark measure of a cohort study. It compares the incidence of disease in the exposed group to the incidence in the non-exposed group. **High-Yield Clinical Pearls for NEET-PG:** * **Cohort Study:** Proceeds from **Cause to Effect**. Best for rare exposures. * **Case-Control Study:** Proceeds from **Effect to Cause**. Best for rare diseases. * **Incidence** can *only* be calculated in Cohort studies (and Randomized Controlled Trials). * If a disease is rare, the Odds Ratio (from a case-control study) numerically approximates the Relative Risk.

Q: The usefulness of a screening test in a community depends on its:

Predictive value. **Explanation:** The usefulness of a screening test in a community or clinical setting is primarily determined by its **Predictive Value**. While sensitivity and specificity are inherent properties of the test itself, the predictive value tells us how well the test performs in a real-world population. 1. **Why Predictive Value is Correct:** Predictive value (Positive and Negative) indicates the probability that a patient actually has (or does not have) the disease given a specific test result. In a community setting, the **Positive Predictive Value (PPV)** is the most critical metric because it determines the "yield" of the screening program—i.e., how many people flagged as "positive" truly require further diagnostic workup and treatment. 2. **Why Other Options are Incorrect:** * **Sensitivity and Specificity:** These are **intrinsic properties** of a test. They do not change based on the population being tested. While they determine the test's accuracy, they do not account for the **prevalence** of the disease, which is a key factor in community application. * **Reliability (Precision):** This refers to the ability of a test to give consistent results when repeated under the same conditions. While necessary for a good test, it does not measure the clinical usefulness or diagnostic power in a population. **High-Yield NEET-PG Pearls:** * **Prevalence Connection:** Predictive value is heavily dependent on the prevalence of the disease. If prevalence increases, PPV increases and NPV decreases. * **Sensitivity vs. Specificity:** Sensitivity is used to "Rule Out" disease (SnNout), while Specificity is used to "Rule In" disease (SpPin). * **Screening Goal:** For a rare disease in a community, a test with high specificity is often preferred to minimize false positives and avoid overwhelming the healthcare system.

Question 1

Formation of an etiological hypothesis is a key step in which type of epidemiology?

Accepted Answer

Descriptive Epidemiology

Answer

Analytical Epidemiology

Answer

Experimental Epidemiology

Answer

None of the above

Question 2

Randomization is useful to eliminate which of the following?

Accepted Answer

Confounding factors

Answer

Observer bias

Answer

Patient bias

Answer

Sampling bias

Question 3

If a Hemoccult test is negative for screening of colonic cancer, no further test is done. If the Hemoccult test is positive, the individual will have a second stool sample tested with Hemoccult II test. If this second sample is positive for blood, the individual will be referred for more extensive evaluation. What is the effect of this screening method on net sensitivity and net specificity?

Accepted Answer

Net sensitivity is decreased and net specificity is increased.

Answer

Net sensitivity and net specificity are both increased.

Answer

Net sensitivity is increased and net specificity is decreased.

Answer

Net sensitivity remains the same and net specificity is increased.

Question 4

What is the first step in the investigation of an epidemic?

Accepted Answer

Verification of the diagnosis

Answer

Source identification

Answer

Confirmation of the existence of an epidemic

Answer

Formation of a hypothesis

Question 5

Under AFP Surveillance, what is the follow-up examination period for residual paralysis?

Accepted Answer

60 days from onset of paralysis

Answer

15 days from onset of paralysis

Answer

33 days from onset of paralysis

Answer

90 days from onset of paralysis

Question 6

What is the most common cancer affecting both males and females worldwide?

Accepted Answer

Lung cancer

Answer

Cancer of the pancreas

Answer

Buccal mucosa cancer

Answer

Colo-rectal cancer

Question 7

Which of the following is NOT evaluated by a cohort study?

Accepted Answer

Odds ratio

Answer

Incidence

Answer

Attributable risk

Answer

Relative risk

Question 8

In a school with 100 unimmunized children, 1 child developed measles on January 1st. Following this, 35 children developed measles, with 3 cases occurring on January 3rd and the remaining cases appearing 2-3 weeks later. What is the secondary attack rate (SAR)?

Accepted Answer

33.30%

Answer

35%

Answer

32%

Answer

36.50%

Question 9

The usefulness of a screening test in a community depends on its:

Accepted Answer

Predictive value

Answer

Sensitivity

Answer

Specificity

Answer

Reliability

Question 10

What is the definition of 'lead time' in epidemiology?

Accepted Answer

The time between the first possible point of detection and the usual time of diagnosis.

Answer

The time between disease onset and the first critical diagnosis.

Answer

The time between disease onset and the first possible point of detection.

Answer

The time between the first possible point of detection and a final critical point.

Epidemiology — MCQs

Epidemiology — MCQs

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