Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 691: Using a seatbelt is an example of which level of prevention?

A. Primary
B. Secondary (Correct Answer)
C. Tertiary
D. Rehabilitation

Explanation: ### Explanation The correct answer is **Secondary Prevention**. In the context of injury epidemiology, levels of prevention are categorized based on the timing of the intervention relative to the "event" (the crash) and the "injury." 1. **Why Secondary Prevention is Correct:** Secondary prevention aims to **reduce the severity** of a disease or injury once the event has already started. A seatbelt does not prevent the car accident (the event) from occurring; rather, it intervenes *during* the crash to minimize the impact and prevent serious injury or death. In injury control, interventions that reduce the severity of trauma during the "human-machine-environment" interaction are classified as secondary. 2. **Why Other Options are Incorrect:** * **Primary Prevention:** This aims to prevent the occurrence of the event entirely. In this context, primary prevention would be measures like traffic signals, speed limits, or anti-lock braking systems (ABS) that prevent the crash from happening. * **Tertiary Prevention:** This focuses on limiting disability and complications after the injury has occurred. Examples include emergency medical services (EMS), trauma surgery, and long-term physical therapy. * **Rehabilitation:** This is a component of tertiary prevention aimed at restoring the individual to their maximum functional capacity. ### High-Yield Pearls for NEET-PG: * **Haddon’s Matrix:** This is the standard framework for injury prevention. * **Pre-event (Primary):** Prevents the crash (e.g., sober driving). * **Event (Secondary):** Prevents injury during the crash (e.g., **Seatbelts, Airbags, Helmets**). * **Post-event (Tertiary):** Prevents death/disability after injury (e.g., Golden Hour care). * **Key Distinction:** If a measure stops the disease/event from starting, it is Primary. If it detects it early or reduces its immediate impact, it is Secondary.

Question 692: Bias can be eliminated by all except?

A. Matching
B. Blinding
C. Randomization
D. Multivariate analysis (Correct Answer)

Explanation: ### Explanation The core of this question lies in distinguishing between **Bias** and **Confounding**. While often discussed together, they are handled differently in epidemiological studies. **1. Why Multivariate Analysis is the Correct Answer:** Multivariate analysis is a statistical tool used to control for **confounding variables**, not bias. Bias is a systematic error in the design, conduct, or analysis of a study that results in a mistaken estimate of an exposure's effect on the risk of disease. Once bias is introduced into a study, it cannot be "adjusted" or "removed" statistically during the analysis phase. In contrast, confounding can be managed during the analysis phase using multivariate models or stratification. **2. Analysis of Incorrect Options (Methods to Eliminate Bias):** * **Matching (Option A):** Used primarily in Case-Control studies to eliminate **selection bias** and control for known confounders by ensuring that the cases and controls are similar with respect to specific variables (e.g., age, sex). * **Blinding (Option B):** This is the gold standard for eliminating **measurement/observer bias**. By keeping the participant (single), investigator (double), or data analyst (triple) unaware of the group assignment, subjective prejudices are removed. * **Randomization (Option C):** Known as the "heart" of a Randomized Controlled Trial (RCT), it eliminates **selection bias** by ensuring every participant has an equal chance of being assigned to any group, thereby balancing both known and unknown confounders. **Clinical Pearls for NEET-PG:** * **Bias** must be prevented at the **design and data collection stage**. * **Confounding** can be managed at both the **design stage** (Matching, Randomization, Restriction) and the **analysis stage** (Multivariate analysis, Stratification). * **Recall Bias** is most common in Case-Control studies, while **Loss-to-follow-up (Attrition) Bias** is common in Cohort studies.

Question 693: Screening for a disease is an application of which of the following concepts?

A. Acute disease
B. Disease with lag time (Correct Answer)
C. Communicable diseases
D. Low case fatality

Explanation: ### Explanation **1. Why "Disease with lag time" is correct:** Screening is the process of identifying unrecognized diseases in apparently healthy individuals. For screening to be effective and ethically justifiable, a disease must have a **Lead Time** (often referred to here as lag time). This is the period between the early detection of a disease (by screening) and its usual time of clinical diagnosis. If a disease progresses too rapidly without a detectable preclinical phase, screening offers no benefit because there is no window of opportunity to intervene and alter the outcome. **2. Analysis of Incorrect Options:** * **A. Acute disease:** These typically have a rapid onset and short duration. There is usually no significant preclinical phase, making screening impractical. * **C. Communicable diseases:** While some communicable diseases (like HIV or TB) are screened, "communicability" is not the underlying epidemiological *requirement* for screening. Many non-communicable diseases (like Cervical Cancer) are the primary targets of screening programs. * **D. Low case fatality:** Screening is actually prioritized for diseases with **high morbidity or mortality** (high case fatality) where early intervention can significantly save lives or reduce disability. **3. NEET-PG High-Yield Pearls:** * **Iceberg Phenomenon:** Screening aims to uncover the "submerged portion" of the iceberg (pre-symptomatic cases). * **Wilson and Jungner Criteria:** The gold standard criteria for a screening program; it states the condition should be an important health problem with a recognizable latent stage. * **Lead Time Bias:** An error in survival analysis where screening appears to prolong survival simply because the disease was detected earlier, not because the patient lived longer from the biological onset. * **Yield:** The amount of previously undiagnosed disease estimated by the screening test.

Question 694: What is the major purpose of randomization in a clinical trial?

A. To facilitate double blinding
B. To help ensure the study subjects are representative of the general population
C. To ensure the groups are comparable in baseline characteristics
D. To reduce selection bias in allocation of treatment (Correct Answer)

Explanation: **Explanation:** **Randomization** is the "heart" of a Randomized Controlled Trial (RCT). Its primary purpose is to eliminate **selection bias** by ensuring that the investigator cannot influence which participant receives which treatment. By using a random process (like computer-generated tables), every participant has an equal chance of being assigned to any group, thereby preventing the researcher from consciously or unconsciously picking "healthier" patients for a specific intervention. **Analysis of Options:** * **Option D (Correct):** Randomization specifically addresses the **allocation process**. It ensures that the assignment is objective, thus neutralizing selection bias. * **Option C (Incorrect):** While randomization *aims* to make groups comparable regarding baseline characteristics (both known and unknown confounders), this is a **consequence** of the process, not its primary procedural definition. Note: If a question asks for the "primary advantage" regarding confounding, this would be the answer; however, the "major purpose" of the act of randomizing is to remove bias in allocation. * **Option A (Incorrect):** Blinding (Masking) is a separate procedure used to reduce *ascertainment* or *information bias*. While randomization facilitates blinding, it is not the reason we randomize. * **Option B (Incorrect):** Representativeness is achieved through **Random Sampling**, not Randomization. Randomization deals with internal validity, while sampling deals with external validity (generalizability). **High-Yield Pearls for NEET-PG:** * **Randomization:** Eliminates Selection Bias and controls for **Unknown Confounders** (the only method to do so). * **Blinding:** Eliminates Observer/Information Bias. * **Allocation Concealment:** The mechanism (e.g., sealed envelopes) used to implement randomization; it prevents selection bias *before* the intervention begins. * **Gold Standard:** The RCT is the gold standard for establishing **causality**.

Question 695: In a screening test for Carcinoma Breast, the sensitivity is 90% and specificity is 98%. What is the chance of a patient with Carcinoma breast to be detected negative in screening conducted in two consecutive years?

A. 1/10
B. 1/10
C. 1/100 (Correct Answer)
D. 1/100

Explanation: ### Explanation **1. Understanding the Correct Answer (C: 1/100)** The question asks for the probability of a patient with the disease being detected as **negative** (a False Negative) in two consecutive screening rounds. * **Sensitivity** is the ability of a test to correctly identify those with the disease. Here, Sensitivity = 90% (0.9). * **False Negative Rate (FNR)** is the probability that a person with the disease will test negative. It is calculated as: $1 - \text{Sensitivity}$. * $FNR = 1 - 0.9 = 0.1$ (or $1/10$). * **Consecutive Events:** Since the screenings in two different years are independent events, we use the **multiplication rule** of probability. * Probability of testing negative in Year 1 AND Year 2 = $FNR \times FNR$ * $1/10 \times 1/10 = \mathbf{1/100}$. **2. Analysis of Incorrect Options** * **Option A & B (1/10):** This represents the False Negative Rate for a **single** screening test. It fails to account for the second consecutive year. * **Option D (1/100):** While the numerical value is correct, in a standard MCQ format, only one specific option is designated as the key. (Note: In the provided prompt, C and D are identical; mathematically, 1/100 is the only correct derivation). **3. High-Yield Clinical Pearls for NEET-PG** * **Sensitivity (True Positive Rate):** High sensitivity is required for **screening tests** to ensure fewer cases are missed (low False Negatives). * **Specificity (True Negative Rate):** High specificity is required for **confirmatory tests** to avoid unnecessary treatment (low False Positives). * **Relationship:** * False Negative Rate = $1 - \text{Sensitivity}$ (Type II Error / $\beta$) * False Positive Rate = $1 - \text{Specificity}$ (Type I Error / $\alpha$) * **Screening Interval:** Repeated screening (serial testing) increases the "Net Sensitivity" but decreases the "Net Specificity" of the diagnostic process.

Question 696: What is the best level of prevention for Breast cancer?

A. Specific protection
B. Early diagnosis and treatment (Correct Answer)
C. Disability limitation
D. Rehabilitation

Explanation: ### Explanation The correct answer is **Early diagnosis and treatment** because breast cancer prevention currently relies primarily on **Secondary Prevention**. **1. Why "Early diagnosis and treatment" is correct:** In epidemiology, secondary prevention aims to detect a disease in its earliest stages (pre-symptomatic phase) to improve prognosis and reduce mortality. Since the exact etiology of breast cancer is multifactorial (genetic, hormonal, and environmental) and cannot be entirely prevented, the "best" strategy is screening. Methods like **Mammography** and **Breast Self-Examination (BSE)** are designed for early detection, which allows for curative treatment before metastasis occurs. **2. Why other options are incorrect:** * **Specific Protection (Primary Prevention):** This involves measures like vaccination or specific nutritional supplements to prevent the *onset* of disease. While lifestyle changes (reducing alcohol, maintaining BMI) help, there is no "specific" vaccine or chemoprophylaxis that universally prevents breast cancer. * **Disability Limitation (Tertiary Prevention):** This occurs when the disease has already progressed. It focuses on limiting further damage (e.g., a radical mastectomy to prevent local spread). * **Rehabilitation (Tertiary Prevention):** This involves restoring function after treatment, such as physiotherapy for lymphedema or reconstructive surgery. **3. NEET-PG High-Yield Pearls:** * **Levels of Prevention:** * *Primordial:* Prevention of risk factors (e.g., discouraging smoking in youth). * *Primary:* Action taken prior to the onset of disease (e.g., Immunization). * *Secondary:* Action which halts the progress of a disease (e.g., Screening tests like Pap smear for Cervical Cancer or Sputum microscopy for TB). * **Breast Cancer Screening:** Mammography is the gold standard for secondary prevention in women over 40-50 years. * **Rule of Thumb:** If the question mentions "Screening" or "Early detection," the answer is almost always **Secondary Prevention**.

Question 697: Which of the following indicators is NOT included in the Human Development Index (HDI)?

A. Mean years of schooling
B. Life expectancy at age 1 (Correct Answer)
C. Real GDP per capita
D. Adult literacy rate

Explanation: **Explanation:** The **Human Development Index (HDI)** is a composite statistical tool used by the UNDP to measure a country's overall achievement in its social and economic dimensions. It consists of **three dimensions** and **four indicators**. **Why "Life expectancy at age 1" is the correct answer:** The HDI uses **Life Expectancy at Birth** as the indicator for the "Long and Healthy Life" dimension. "Life expectancy at age 1" is a component of the **Physical Quality of Life Index (PQLI)**, not the HDI. This is a common point of confusion in NEET-PG; remember that PQLI includes Infant Mortality Rate (IMR), Life Expectancy at age 1, and Literacy, whereas HDI focuses on birth-level data and economic productivity. **Analysis of Incorrect Options:** * **Mean years of schooling:** This is a current indicator for the "Knowledge" dimension (Education Index). It measures the average number of years of education received by people ages 25 and older. * **Real GDP per capita:** This represents the "Standard of Living" dimension. In the modern HDI formula, it is specifically measured as **GNI (Gross National Income) per capita (PPP $)**. * **Adult literacy rate:** While the HDI was updated in 2010 to use "Mean years" and "Expected years" of schooling, Adult Literacy was the primary indicator for the education dimension in the original formula. In the context of "NOT included," Life expectancy at age 1 remains the most definitive outlier as it belongs to a different index entirely. **High-Yield Clinical Pearls for NEET-PG:** * **HDI Components:** 1. Life Expectancy at Birth, 2. Mean years of schooling, 3. Expected years of schooling, 4. GNI per capita. * **HDI Range:** 0 to 1 (Higher is better). * **PQLI Components:** 1. Infant Mortality Rate (IMR), 2. Life Expectancy at age 1, 3. Basic Literacy (at age 15). * **PQLI Range:** 0 to 100. * **Key Distinction:** HDI includes **Income** (GNI/GDP), whereas PQLI **does not** include any economic indicators.

Question 698: Which of the following statements is NOT true about the term 'disease control'?

A. Interruption of the transmission of disease (Correct Answer)
B. Reducing the incidence of disease
C. Agent is permitted to persist at low levels
D. Focus is on primary and/or secondary prevention

Explanation: ### Explanation In epidemiology, it is crucial to distinguish between disease **control**, **elimination**, and **eradication**. **Why Option A is the Correct Answer (The "Not True" Statement):** **Interruption of the transmission of disease** is the defining characteristic of **Elimination**, not control. In the control phase, the disease continues to transmit within the community, but at a level that is no longer considered a significant public health problem. Elimination refers to achieving "zero incidence" in a specific geographic area (e.g., Polio elimination in India), whereas control is merely the reduction of the disease burden. **Analysis of Other Options:** * **Option B (Reducing incidence):** This is a primary objective of disease control. It aims to reduce the number of new cases (incidence), the total number of existing cases (prevalence), and the associated morbidity/mortality. * **Option C (Agent persists at low levels):** In the control stage, the infectious agent is still present in the environment or population. It is not wiped out; it is simply managed. * **Option D (Focus on prevention):** Disease control relies heavily on **Primary prevention** (e.g., immunization, health promotion) to reduce incidence and **Secondary prevention** (e.g., early diagnosis and treatment) to reduce prevalence and transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Control:** Reduction in incidence, prevalence, morbidity, or mortality to locally acceptable levels. * **Elimination:** Interruption of transmission (zero incidence) in a **defined geographic area** (e.g., Neonatal Tetanus). * **Eradication:** Permanent reduction to **zero worldwide**; the agent is completely extinct in nature (e.g., Smallpox, 1980). * **Monitoring:** The continuous performance and analysis of routine measurements. * **Surveillance:** Continuous scrutiny of all aspects of occurrence and spread of a disease.

Question 699: Regarding the epidemiology of AIDS, all the following statements are true EXCEPT:

A. Maternofetal transmission is the most common mode of transmission. (Correct Answer)
B. In India, AIDS is mainly caused by HIV-1.
C. Intravenous drug abuse increases the risk of transmission.
D. Medical personnel are at higher risk of acquiring HIV infection.

Explanation: **Explanation** The correct answer is **A**, as it is a false statement. Globally and in India, the **most common mode of HIV transmission is sexual contact** (specifically heterosexual transmission in India, accounting for over 85% of cases). While maternofetal (vertical) transmission is a significant route, it is not the most frequent. **Analysis of Options:** * **Option A (False):** Sexual transmission remains the primary driver of the epidemic. Vertical transmission occurs in about 15-45% of infants born to untreated HIV-positive mothers but is significantly lower in the overall epidemiological distribution. * **Option B (True):** HIV-1 is the predominant subtype globally and in India. HIV-2 is largely restricted to West Africa, though cases are occasionally reported in Western and Southern India. * **Option C (True):** Intravenous drug use (IDU) is a high-risk behavior due to the direct sharing of contaminated needles, leading to rapid transmission within communities (common in North-East India). * **Option D (True):** Medical personnel face an occupational hazard through accidental needle-stick injuries or exposure to infected blood/body fluids, placing them at a higher risk compared to the general non-exposed population. **High-Yield Clinical Pearls for NEET-PG:** * **Risk of Transmission:** The risk of transmission via a single needle-stick injury from an HIV-positive source is approximately **0.3%**. For Hepatitis B, it is much higher (up to 30%). * **Post-Exposure Prophylaxis (PEP):** Should be started as soon as possible, ideally within **2 hours** and no later than **72 hours**, for a duration of **28 days**. * **Window Period:** The time between infection and the appearance of detectable antibodies (usually 2–12 weeks). The **p24 antigen** is the earliest marker detectable. * **Best Screening Test:** ELISA; **Best Confirmatory Test:** Western Blot (though newer NACO guidelines emphasize rapid tests for diagnosis).

Question 700: A group of smokers was followed up for 10 years to determine the incidence of lung cancer. What type of study is this?

A. Retrospective cohort
B. Prospective cohort (Correct Answer)
C. Case control study
D. Randomized control trial

Explanation: ### Explanation **Correct Answer: B. Prospective Cohort** The study described is a **Prospective Cohort study** because it begins with a group of individuals (the cohort) who are currently free of the disease but differ in their exposure status (smokers). These individuals are followed forward in time (**longitudinal follow-up**) to observe the development of the outcome (lung cancer). In epidemiology, the hallmark of a cohort study is the direction of inquiry: **from Cause (Exposure) to Effect (Outcome).** Since the follow-up occurs from the present into the future, it is "prospective." --- ### Why other options are incorrect: * **A. Retrospective Cohort:** While this also moves from exposure to outcome, it uses past records (e.g., employment files from 1990) to determine exposure and looks at outcomes that have already occurred by the time the study starts. * **C. Case-Control Study:** This study design moves backward from **Effect to Cause**. It starts with people who already have lung cancer (cases) and compares them to those who don't (controls) to look for past smoking habits. * **D. Randomized Control Trial (RCT):** This is an experimental study where the investigator intervenes (e.g., gives a drug). In the question, the investigator is merely observing natural behavior (smoking), making it an observational study, not a trial. --- ### NEET-PG High-Yield Pearls: * **Incidence:** Cohort studies are the only observational studies that can directly calculate the **Incidence** of a disease. * **Risk Measure:** The primary measure of association in a cohort study is **Relative Risk (RR)** or Risk Ratio. * **Best for Rare Exposures:** Cohort studies are ideal for studying rare exposures (e.g., a specific chemical in a factory), whereas Case-Control studies are best for rare diseases. * **Mnemonic:** **C**ohort = **C**ause to Effect; **C**ase-Control = **C**onsequence to Cause.

Practice by Chapter

Principles of Epidemiology

Practice Questions

Measures of Disease Frequency

Practice Questions

Epidemiological Study Designs

Practice Questions

Descriptive Epidemiology

Practice Questions

Analytical Epidemiology

Practice Questions

Experimental Epidemiology

Practice Questions

Screening for Disease

Practice Questions

Surveillance Systems

Practice Questions

Investigation of an Epidemic

Practice Questions

Association and Causation

Practice Questions

Modern Epidemiological Methods

Practice Questions

Critical Appraisal of Epidemiological Studies

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free