Epidemiology — MCQs

Epidemiology Indian Medical PG Practice Questions and MCQs

Question 751: Which of the following is NOT true about cohort studies?

A. They are prospective.
B. They are useful for rare diseases. (Correct Answer)
C. They are necessary for calculating incidence.
D. They are costly.

Explanation: **Explanation:** In epidemiology, a **Cohort Study** is an observational analytical study that starts with a group of exposed and non-exposed individuals and follows them forward in time to see who develops the disease. **Why Option B is the correct answer (NOT true):** Cohort studies are **not** suitable for rare diseases. Because these studies follow people over time to see if they develop a condition, if the disease is rare (e.g., a specific rare cancer), the researcher would need to follow an impractically large population for a very long duration to observe even a few cases. **Case-control studies** are the preferred design for rare diseases as they start with people who already have the condition. **Analysis of Incorrect Options:** * **Option A (They are prospective):** This is true. Most cohort studies move forward from cause to effect. (Note: Retrospective cohorts exist but the logic remains "exposure to outcome"). * **Option C (Necessary for calculating incidence):** This is true. Since we start with a disease-free population and monitor new cases over time, cohort studies are the only observational design that directly calculates **Incidence** and **Relative Risk (RR)**. * **Option D (They are costly):** This is true. Due to long follow-up periods, large sample sizes, and the need for repeated testing/staffing, they are significantly more expensive than cross-sectional or case-control studies. **High-Yield NEET-PG Pearls:** * **Direction:** Forward (Exposure $\rightarrow$ Outcome). * **Best for:** Rare **exposures** (e.g., occupational hazards). * **Key Metric:** Relative Risk (RR) and Attributable Risk (AR). * **Major Bias:** Selection bias and **Attrition bias** (loss to follow-up). * **Mnemonic:** "C"ohort = "C"ause to effect; "C"alculates In"c"idence.

Question 752: Maternal mortality rate is expressed as:

A. 1000 live births
B. 100,000 live births (Correct Answer)
C. 1000 pregnancies
D. 100 pregnancies

Explanation: ### Explanation **1. Understanding the Correct Answer (Option B)** The **Maternal Mortality Ratio (MMR)** is defined as the number of maternal deaths during a given time period per **100,000 live births** during the same period. It measures the obstetric risk associated with each pregnancy. *Note on Terminology:* While the question uses the term "Rate," in strict epidemiological terms, this is a **Ratio** because the numerator (maternal deaths) is not a subset of the denominator (live births). However, in many competitive exams and official reports, the term "Maternal Mortality Rate" is frequently used interchangeably with "Ratio." **2. Analysis of Incorrect Options** * **Option A (1,000 live births):** This is the standard denominator for the **Infant Mortality Rate (IMR)**, Neonatal Mortality Rate, and Crude Birth Rate. Using this for maternal mortality would result in very small, decimal figures that are difficult to track. * **Options C & D (Pregnancies):** Maternal mortality is calculated based on "live births" rather than "total pregnancies" because live births are more accurately recorded. Total pregnancies (which include abortions, miscarriages, and stillbirths) are difficult to track accurately in many populations. **3. NEET-PG High-Yield Clinical Pearls** * **Definition of Maternal Death:** Death of a woman while pregnant or within **42 days** of delivery, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy. * **Late Maternal Death:** Death occurring between **42 days and one year** after delivery. * **Maternal Mortality Rate (True Rate):** If specifically asked for the "Rate" (not Ratio) in a strict sense, the denominator is **1,000 women of reproductive age (15-49 years)**. * **Most Common Cause:** In India, the leading cause of maternal mortality is **Obstetric Hemorrhage** (specifically Postpartum Hemorrhage/PPH). * **SDG Target:** The Sustainable Development Goal (SDG) target is to reduce the global MMR to less than **70 per 100,000 live births** by 2030.

Question 753: Which of the following is best to compare the vital statistics of countries?

A. Crude death and birth rates
B. Age standardized death rate (Correct Answer)
C. Proportional mortality rate
D. Age specific death rate

Explanation: **Explanation** The **Age Standardized Death Rate (ASDR)** is the gold standard for comparing the health status and vital statistics of different populations. This is because age is the most significant determinant of mortality; a population with a higher proportion of elderly individuals will naturally have more deaths than a younger population, even if health services are superior. Standardization (Direct or Indirect) removes the confounding effect of different age structures, allowing for a "fair" or "apples-to-apples" comparison between countries. **Why other options are incorrect:** * **Crude Death and Birth Rates:** These are influenced heavily by the age and sex composition of the population. A developed country with an aging population may have a higher crude death rate than a developing country with a young population, which is misleading. * **Proportional Mortality Rate:** This measures the proportion of total deaths due to a specific cause (e.g., CVD). It does not reflect the actual risk of dying in a population and is used to identify the relative importance of a disease within a group, not for cross-country comparison. * **Age-Specific Death Rate:** While accurate for a specific age group (e.g., 5–10 years), it only provides a partial picture. It cannot be used to compare the overall health status of entire nations without being integrated into a standardized index. **High-Yield Pearls for NEET-PG:** * **Standardized Mortality Ratio (SMR):** Used in indirect standardization; it is the ratio of Observed Deaths to Expected Deaths. * **Indicator of Choice:** While ASDR is best for comparison, the **Infant Mortality Rate (IMR)** is considered the most sensitive indicator of a country’s overall health status and socio-economic development. * **Life Expectancy at Birth:** The best single indicator of the "level of living" and overall health of a population.

Question 754: What determines the diagnostic accuracy of a test?

A. Sensitivity
B. Specificity
C. Predictive value (Correct Answer)
D. None of the above

Explanation: **Explanation:** The **Predictive Value** (Positive and Negative) is the most clinically relevant measure of diagnostic accuracy because it determines the probability that a test result correctly reflects the true disease status of an individual patient. While sensitivity and specificity are inherent properties of the test itself, the predictive value tells a clinician how much they can trust a result in a real-world setting. * **Why Predictive Value is correct:** Diagnostic accuracy in a clinical context refers to the test's ability to correctly identify diseased and non-diseased individuals within a population. Predictive values are influenced by the **prevalence** of the disease. A test with high sensitivity is useless if its Positive Predictive Value (PPV) is low due to low disease prevalence, as most "positives" would be false alarms. * **Why Sensitivity is incorrect:** Sensitivity measures the ability of a test to correctly identify those *with* the disease (True Positive Rate). It is used for screening (SNOUT) but does not account for false positives, thus it cannot alone define overall diagnostic accuracy. * **Why Specificity is incorrect:** Specificity measures the ability to correctly identify those *without* the disease (True Negative Rate). It is used for confirmation (SPIN) but does not account for false negatives. **High-Yield Clinical Pearls for NEET-PG:** 1. **Prevalence Relationship:** If prevalence increases, **PPV increases** and **NPV decreases**. Sensitivity and Specificity remain unchanged. 2. **Screening vs. Diagnosis:** Use a high-sensitivity test to "Rule Out" (Screening) and a high-specificity test to "Rule In" (Diagnosis). 3. **Likelihood Ratio:** This is considered the best tool for measuring diagnostic accuracy independent of prevalence, but among the given options, Predictive Value is the standard clinical measure.

Question 755: Which Indian state has a crude birth rate higher than the national average?

A. West Bengal
B. Maharashtra
C. Rajasthan (Correct Answer)
D. Andhra Pradesh

Explanation: **Explanation:** The **Crude Birth Rate (CBR)** is defined as the number of live births per 1,000 mid-year population in a given year. It is a sensitive indicator of fertility levels and population growth. According to the latest **Sample Registration System (SRS) Bulletin**, the national average CBR for India stands at approximately **19.5 per 1,000 population**. **Why Rajasthan is Correct:** Rajasthan consistently reports a CBR (approx. **23.5**) significantly higher than the national average. This is attributed to a higher Total Fertility Rate (TFR), lower contraceptive prevalence in rural pockets, and socio-demographic factors prevalent in the "BIMARU" states (Bihar, Madhya Pradesh, Rajasthan, and Uttar Pradesh), all of which typically exceed national fertility benchmarks. **Analysis of Incorrect Options:** * **West Bengal:** Has successfully transitioned to a low CBR (approx. **14.2**), well below the national average, due to effective family welfare programs. * **Maharashtra:** As a more urbanized and socio-economically advanced state, its CBR (approx. **15.3**) remains lower than the national mean. * **Andhra Pradesh:** One of the first southern states to achieve replacement-level fertility; its CBR (approx. **15.9**) is significantly lower than the national average. **High-Yield Pearls for NEET-PG:** * **Highest CBR in India:** Bihar (approx. 25.5). * **Lowest CBR in India:** Kerala / Andaman & Nicobar Islands. * **Replacement Level Fertility (TFR):** 2.1 (India’s current TFR has reached 2.0 as per NFHS-5). * **CBR Formula:** (Number of live births during the year / Mid-year population) × 1000.

Question 756: According to the latest WHO classification and measurement of disability, what is the correct terminology?

A. IDEAS
B. ICD (Correct Answer)
C. ICIDH-II
D. WHO DAS I

Explanation: **Explanation:** The classification of disability has evolved significantly. According to the current WHO framework, the **ICD (International Classification of Diseases)** is the standard for defining and measuring health and health-related states. Specifically, the **ICD-11** now incorporates the concepts of functioning and disability directly into its coding system, working in tandem with the **ICF (International Classification of Functioning, Disability and Health)**. This integrated approach allows for a standardized global measurement of health outcomes and disability. **Analysis of Options:** * **ICD (Correct):** It is the latest global standard for health data, clinical documentation, and aggregation. The current 11th revision (ICD-11) integrates functional status, making it the primary tool for disability measurement in clinical settings. * **IDEAS (Incorrect):** This stands for the *Indian Disability Evaluation and Assessment Scale*. While it is used in India for measuring the severity of mental illness and disability, it is a regional tool, not the latest global WHO classification. * **ICIDH-II (Incorrect):** The *International Classification of Impairments, Disabilities, and Handicaps* (ICIDH) was the old 1980 framework. ICIDH-II was the draft name for its successor, which was eventually finalized and renamed as the **ICF** in 2001. * **WHO DAS I (Incorrect):** The *World Health Organization Disability Assessment Schedule* is a tool used to measure health and disability, but the current version is **WHODAS 2.0**, which is based on the ICF framework. **High-Yield Clinical Pearls for NEET-PG:** * **ICF Framework:** Focuses on three levels: **Body Functions/Structures**, **Activities** (limitations), and **Participation** (restrictions). * **Old vs. New:** The old sequence was *Disease → Impairment → Disability → Handicap*. The new ICF model is **biopsychosocial**, emphasizing "Functioning" rather than just "Disability." * **ICD-11:** Officially came into effect on January 1, 2022.

Question 757: According to epidemiological studies, which dietary factor has been found to be most protective against carcinoma of the colon?

A. High fiber diet (Correct Answer)
B. Low fat diet
C. Low selenium diet
D. Low protein diet

Explanation: **Explanation:** **1. Why High Fiber Diet is Correct:** Epidemiological evidence consistently identifies a **high-fiber diet** as the most significant protective factor against colorectal carcinoma. Dietary fiber (found in fruits, vegetables, and whole grains) acts through several mechanisms: * **Dilution:** It increases fecal bulk, thereby diluting potential carcinogens (like bile acids) in the colon. * **Transit Time:** It accelerates colonic transit, reducing the duration of contact between the intestinal mucosa and carcinogens. * **Fermentation:** Gut bacteria ferment fiber into **Short-Chain Fatty Acids (SCFAs)** like butyrate, which have anti-inflammatory properties and promote apoptosis in cancerous cells. **2. Analysis of Incorrect Options:** * **B. Low fat diet:** While high intake of saturated animal fats is a known *risk factor* (as it increases bile acid secretion which can be converted into secondary carcinogens), a low-fat diet is considered a preventive strategy rather than the primary "most protective" factor compared to fiber. * **C. Low selenium diet:** This is incorrect because selenium is actually a trace element with antioxidant properties. **Low** levels of selenium are associated with an *increased* risk of various cancers; therefore, a "low selenium diet" would be a risk factor, not protective. * **D. Low protein diet:** There is no strong evidence that a low protein diet is protective. However, a diet high in **processed red meats** is a significant risk factor for colon cancer. **3. High-Yield Clinical Pearls for NEET-PG:** * **Burkitt’s Hypothesis:** Proposed that the high fiber intake in African populations was responsible for their low incidence of colorectal cancer. * **Other Protective Factors:** Physical activity, Aspirin/NSAIDs (via COX-2 inhibition), and adequate Calcium/Vitamin D intake. * **Gold Standard Screening:** Colonoscopy remains the most effective secondary prevention tool for early detection and removal of precancerous polyps.

Question 758: Point prevalence studies tend to overestimate the occurrence of which of the following diseases?

A. Diseases with a high incidence
B. Diseases with a long duration (Correct Answer)
C. Diseases with a high mortality
D. Diseases with a short duration

Explanation: **Explanation** The correct answer is **B. Diseases with a long duration.** **Understanding the Concept** Prevalence is defined by the formula: **Prevalence (P) ≈ Incidence (I) × Duration (D)**. Point prevalence acts like a "snapshot" in time. Because diseases with a long duration (chronic conditions) stay in the population pool for an extended period, they are much more likely to be captured during a single point-in-time survey. Conversely, diseases that resolve quickly (either through cure or death) are often missed by such snapshots, leading to an over-representation of chronic cases in prevalence data. This is known as **Neyman bias** (or length-time bias). **Analysis of Incorrect Options** * **A. Diseases with a high incidence:** Incidence refers to new cases. A disease can have high incidence but very short duration (e.g., Common Cold); in such cases, point prevalence remains low because patients recover quickly. * **C. Diseases with a high mortality:** High mortality reduces the duration of the disease. If a patient dies quickly after onset, they are less likely to be "present" in the population when a prevalence study is conducted. * **D. Diseases with a short duration:** These are underestimated by point prevalence studies because the "window of opportunity" to identify the case is very small. **NEET-PG High-Yield Pearls** * **Incidence** is the best indicator for the **etiology** of a disease and the efficacy of prevention programs. * **Prevalence** is the best indicator for **administrative planning** and estimating the burden of chronic diseases. * Prevalence **increases** with: Longer duration, prolongation of life without cure, and in-migration of cases. * Prevalence **decreases** with: High fatality rates, shorter duration, and improved cure rates.

Question 759: What is the definition of relative risk?

A. Incidence of disease among the exposed minus the incidence of disease among the non-exposed
B. Incidence of disease among the exposed plus the incidence of disease among the non-exposed
C. Incidence of disease among the exposed divided by the incidence of disease among the non-exposed (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Relative Risk (RR)**, also known as the Risk Ratio, is a fundamental measure of association in epidemiology, primarily used in **Cohort Studies**. It quantifies the strength of the association between an exposure (e.g., smoking) and an outcome (e.g., lung cancer). 1. **Why Option C is Correct:** Relative Risk is defined as the ratio of the incidence of the disease among the exposed group to the incidence of the disease among the non-exposed group. * **Formula:** $RR = \frac{\text{Incidence among exposed } (I_e)}{\text{Incidence among non-exposed } (I_o)}$ * If $RR > 1$, there is a positive association (the exposure is a risk factor). * If $RR = 1$, there is no association. * If $RR < 1$, the exposure is protective. 2. **Why Other Options are Incorrect:** * **Option A:** This describes **Attributable Risk (AR)** or Risk Difference. It measures the amount of disease incidence that can be attributed to the exposure. * **Option B:** This is a mathematically irrelevant calculation in epidemiology and does not represent any standard risk measure. **High-Yield NEET-PG Pearls:** * **Study Design:** RR is calculated from Cohort studies (Prospective). It cannot be calculated directly from Case-Control studies; for those, we use **Odds Ratio (OR)**. * **Strength of Association:** RR is the best indicator of the strength of the association between a cause and an effect. * **Attributable Risk (AR):** Indicates the "public health impact" and suggests how much disease can be prevented if the exposure is removed. * **Population Attributable Risk (PAR):** Useful for prioritizing public health programs by calculating the risk reduction in the total population.

Question 760: Which of the following are modes of cholera transmission?

A. Food transmission
B. Vaccination gives 90% efficiency
C. Healthy carrier (Correct Answer)
D. Chlorination is not effective

Explanation: **Explanation:** Cholera, caused by *Vibrio cholerae*, is primarily transmitted through the **fecal-oral route**. In the context of epidemiology, the **Healthy Carrier** plays a critical role in transmission. These are individuals who harbor the pathogen and can excrete it in their stools for 7–14 days but do not manifest clinical symptoms. Because they are asymptomatic, they move freely in the community, serving as a silent reservoir and a major source of environmental contamination. **Analysis of Options:** * **Healthy Carrier (Correct):** In cholera, for every one severe clinical case, there are approximately 50–100 asymptomatic (healthy) carriers (for El Tor biotype). They are the main "propagators" of an epidemic. * **Food transmission:** While cholera is transmitted via contaminated food and water, the question asks for the *mode* or *source* characteristic. Between a general vehicle (food) and a specific epidemiological reservoir (carrier), the carrier status is a more specific "mode" of maintaining the infection chain in a population. * **Vaccination efficiency:** Current oral cholera vaccines (OCVs) like Shanchol or Dukoral provide roughly 50–65% protection over 3–5 years, not 90%. * **Chlorination:** This is actually the most effective method for disinfecting water against *V. cholerae*. A free residual chlorine level of 0.5 mg/L is highly effective. **NEET-PG High-Yield Pearls:** * **Reservoir:** Man is the only known reservoir. * **Case-to-Carrier Ratio:** 1:10 for Classical cholera; 1:50 to 1:100 for El Tor. * **Incubation Period:** Very short (1–5 days), leading to "explosive" epidemics. * **Gold Standard Diagnosis:** Stool culture on **TCBS medium** (Thiosulfate Citrate Bile Salts Sucrose). * **Stool Appearance:** "Rice water stools" with a fishy odor.

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