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PGIM MD Community Medicine study materials
PGIM MD Community Medicine study resources

PGIM MD Community Medicine practice questions

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Question 1Community Medicine

In a community-based cross-sectional survey, the prevalence of hypertension is reported as 24%. Which measure of disease frequency does this represent?

  1. Cumulative incidence
  2. Incidence rate
  3. Case fatality rate
  4. Point prevalence proportion Correct answer.

Explanation

Prevalence proportion expresses the number of existing cases of a disease in a defined population at a specified time divided by the total population at risk. A single survey capturing current hypertension status yields a point prevalence. Incidence measures new cases over a period and requires follow-up, which a cross-sectional design does not provide.

Question 2Community Medicine

A screening test for a disease with low prevalence in the community is applied to a general population sample. Compared with using the same test in a high-prevalence clinic population, the positive predictive value in the community will most likely be:

  1. Higher, because sensitivity increases
  2. Lower, because prevalence is lower Correct answer.
  3. Higher, because specificity increases
  4. Unchanged, because sensitivity is fixed

Explanation

Positive predictive value depends on both test characteristics and disease prevalence. As prevalence falls, the proportion of positive results that are false positives rises, so PPV falls even when sensitivity and specificity are unchanged. Sensitivity and specificity are intrinsic to the test and do not shift with prevalence.

Question 3Community Medicine

For the overall attack rate in a defined susceptible population during an outbreak, rather than an exposure-specific attack rate, the number of new cases is divided by which denominator?

  1. Number of persons exposed to the implicated agent
  2. Number of susceptible persons at the start of the outbreak only Correct answer.
  3. Total person-years of observation
  4. Number of cases who recovered

Explanation

The attack rate is an incidence proportion: new cases during the outbreak divided by the susceptible population at risk at its start, usually expressed as a percentage. Restricting the denominator to those exposed to a particular agent is appropriate only for an exposure-specific attack rate.

Question 4Community Medicine

A cohort study reports a relative risk of 2.5 with a 95% confidence interval of 1.2 to 5.2. Which interpretation is most appropriate?

  1. The result proves causation because the point estimate exceeds 2
  2. The confidence interval is too wide to permit any conclusion
  3. The association is not statistically significant because the upper limit exceeds 2
  4. The association is statistically significant and exposure is associated with increased risk Correct answer.

Explanation

A confidence interval for relative risk that excludes 1.0 indicates a statistically significant association at the chosen alpha. Here the interval 1.2 to 5.2 lies entirely above 1.0, indicating increased risk among the exposed. Statistical significance does not by itself establish causation.

Question 5Community Medicine

Which study design is most appropriate for estimating the incidence of a rare occupational cancer among workers exposed to a specific solvent?

  1. Prospective cohort study
  2. Case-control study
  3. Cross-sectional survey
  4. Retrospective cohort study Correct answer.

Explanation

Incidence requires following an exposed group over time, which points to a cohort design. Because the cancer is rare and latency is long, a retrospective cohort using historical employment and cancer registry records is more efficient than a prospective cohort. Case-control designs estimate association but cannot directly yield incidence.

Question 6Community Medicine

In a case-control study of lung cancer and smoking, the odds ratio is 4.0. Which statement best describes what this value means?

  1. The risk of lung cancer in smokers is exactly four times that in non-smokers
  2. Smokers have four times the incidence of lung cancer compared with non-smokers
  3. The odds of smoking among cases are four times the odds among controls Correct answer.
  4. Four percent of lung cancer cases are attributable to smoking

Explanation

The odds ratio compares the odds of exposure among cases with the odds of exposure among controls. When the disease is rare, the odds ratio approximates the relative risk, but it is not itself a direct incidence ratio. Interpreting it as an exact risk ratio is only valid under the rare-disease assumption.

Question 7Community Medicine

A randomized controlled trial uses intention-to-treat analysis. What is the main reason for this approach?

  1. It removes the need for a control group
  2. It guarantees that the treatment effect is underestimated
  3. It increases statistical power by excluding non-adherent participants
  4. It preserves the benefit of randomization and avoids bias from selective dropout Correct answer.

Explanation

Intention-to-treat analysis keeps participants in the group to which they were randomized regardless of adherence. This preserves comparability of groups created by randomization and avoids bias introduced when non-adherent participants are excluded. It tends to give a conservative estimate of efficacy.

Question 8Community Medicine

Which measure best quantifies the excess disease burden in a population that could be eliminated if a risk factor were removed?

  1. Relative risk
  2. Odds ratio
  3. Number needed to treat
  4. Population attributable fraction Correct answer.

Explanation

The population attributable fraction estimates the proportion of disease in the population attributable to a given exposure. It combines the strength of association with the prevalence of exposure, reflecting the potential population-level impact of removal. Relative risk and odds ratio describe association only.

Question 9Community Medicine

A community health programme reports that infant mortality rate fell while birth rate remained stable. Which numerator is used in the infant mortality rate?

  1. Deaths in infants under one year of age Correct answer.
  2. Stillbirths plus neonatal deaths
  3. All deaths in children under five years
  4. Deaths in the first 28 days of life only

Explanation

The infant mortality rate counts deaths of children under one year of age in a given year divided by live births in the same year, expressed per 1,000 live births. It is a sensitive indicator of population health and health care quality. Neonatal mortality is a separate measure restricted to the first 28 days.

Question 10Community Medicine

In a district, the crude death rate is high but the age-adjusted death rate is similar to the national average. What is the most likely explanation?

  1. The district has an unusually young population
  2. The standard population is inappropriate
  3. Death registration is incomplete
  4. The district has an older population than the standard Correct answer.

Explanation

Age adjustment removes the effect of differing age structures. A high crude rate with an average adjusted rate indicates the district population is older than the reference, so more deaths occur simply because older people are more numerous. Age-specific rates are not necessarily worse than average.

Question 11Community Medicine

Which of the following is the most appropriate indicator for monitoring the coverage of a maternal and child health programme in a community?

  1. Sex ratio at birth
  2. General fertility rate
  3. Crude birth rate
  4. Proportion of births attended by skilled health personnel Correct answer.

Explanation

Coverage indicators measure the proportion of the target population receiving a service. The proportion of births attended by skilled health personnel directly reflects service coverage for maternal health. Birth rate, sex ratio, and fertility rate are demographic measures not tied to service delivery.

Question 12Community Medicine

A screening programme is being planned for a disease with a long preclinical detectable phase. Which condition most favours the success of screening?

  1. Availability of an effective treatment that improves outcome when started early Correct answer.
  2. Very low prevalence of the disease
  3. High case fatality despite early treatment
  4. Absence of a confirmatory diagnostic test

Explanation

Screening is worthwhile when early detection allows treatment that improves prognosis. A long preclinical phase provides the window for detection, and effective early treatment translates detection into benefit. High case fatality with no effective early treatment undermines screening.

Question 13Community Medicine

Which of the following best describes the purpose of a randomized controlled trial's allocation concealment?

  1. To blind participants to the intervention
  2. To ensure equal numbers in each arm
  3. To prevent investigators from predicting the next assignment Correct answer.
  4. To eliminate confounding by indication during analysis

Explanation

Allocation concealment prevents those enrolling participants from knowing or predicting the next treatment assignment. This protects the randomization sequence from selection bias. Blinding and equal group sizes are related but distinct concepts.

Question 14Community Medicine

In a community survey, the prevalence of diabetes is 10%. What is the odds of having diabetes?

  1. 0.11 Correct answer.
  2. 1.10
  3. 9.00
  4. 0.10

Explanation

Odds equals prevalence divided by one minus prevalence. With prevalence 0.10, the odds are 0.10/0.90, which equals 0.11. Odds and probability diverge as prevalence rises, so they cannot be used interchangeably.

Question 15Community Medicine

Which of the following is the strongest evidence that an observed association between a risk factor and disease is causal?

  1. A relative risk above 3.0 in one study
  2. A single large study with a p-value below 0.05
  3. A consistent dose-response relationship across several studies Correct answer.
  4. An association reported in a widely read textbook

Explanation

Causal inference draws on multiple criteria, including consistency across studies, temporality, biological plausibility, and dose-response. A dose-response gradient replicated across studies strengthens causal inference considerably. Single-study statistical significance or textbook citation is insufficient.

Question 16Community Medicine

A public health team wants to reduce the incidence of a disease with a long latent period by targeting a widely distributed risk factor. Which prevention strategy does this represent?

  1. Secondary prevention
  2. Population (mass) strategy Correct answer.
  3. Tertiary prevention
  4. High-risk strategy

Explanation

The population strategy aims to shift the distribution of a risk factor in the whole community, yielding large aggregate benefit even if individual risk reduction is modest. It suits widely distributed risk factors with long latency. High-risk strategies target individuals with elevated risk.

Question 17Community Medicine

Which of the following is an example of primary prevention in community medicine?

  1. Rehabilitation after stroke
  2. Treatment of hypertension to prevent complications
  3. Immunization against measles in children Correct answer.
  4. Screening for cervical cancer with cytology

Explanation

Primary prevention acts before disease occurs by reducing exposure or increasing resistance. Immunization prevents infection and disease in susceptible children. Screening and treatment of established risk factors operate at secondary or tertiary levels.

Question 18Community Medicine

In a matched case-control study, which analytic approach is most appropriate?

  1. Conditional logistic regression Correct answer.
  2. Kaplan-Meier survival analysis
  3. Simple linear regression
  4. Unmatched chi-square test of exposure

Explanation

Matching creates a dependency between cases and their matched controls, so analysis must account for the matched sets. Conditional logistic regression preserves the matching and estimates the exposure odds ratio correctly. Ignoring matching can bias results.

Question 19Community Medicine

A new test has sensitivity 90% and specificity 95%. In a population with prevalence 1%, what is the approximate positive predictive value?

  1. About 15% Correct answer.
  2. About 90%
  3. About 50%
  4. About 95%

Explanation

With prevalence 1%, of 10,000 people about 100 have disease, and 90 of these test positive. Of the 9,900 without disease, 5% (495) test positive falsely. So PPV is 90/(90+495), roughly 15%. Low prevalence sharply limits predictive value.

Question 20Community Medicine

Which of the following best describes herd immunity?

  1. Immunity acquired after natural infection only
  2. Direct protection conferred by a vaccine to the vaccinated individual
  3. The absence of any susceptible persons in a population
  4. Indirect protection of susceptible individuals when a sufficient proportion of the population is immune Correct answer.

Explanation

Herd immunity is the indirect protection of unvaccinated or susceptible people that arises when enough of the population is immune to interrupt transmission. It depends on the transmissibility of the pathogen and coverage levels. It does not require zero susceptible persons.

Question 21Community Medicine

A district reports a sudden increase in cases of acute diarrhoeal disease over three days. Which first step is most appropriate in the outbreak investigation?

  1. Calculate the population attributable fraction
  2. Verify the diagnosis and confirm that an outbreak exists Correct answer.
  3. Begin a randomized trial of treatment
  4. Immediately publish a causal conclusion in the media

Explanation

Outbreak investigation begins by verifying the diagnosis and confirming that the observed number of cases exceeds expectation. This prevents responding to artefactual increases from reporting changes or laboratory error. Case finding, hypothesis generation, and control measures follow.

Question 22Community Medicine

Which of the following is the most appropriate measure of the burden of premature mortality in a population?

  1. Crude death rate
  2. Case fatality rate
  3. Hospital admission rate
  4. Years of potential life lost Correct answer.

Explanation

Years of potential life lost weights deaths by the remaining life expectancy at the age of death, emphasizing premature mortality. It captures deaths at younger ages more heavily than the crude death rate. Case fatality and admission rates reflect different dimensions of health.

Question 23Community Medicine

In a cross-sectional study, an association is found between physical inactivity and obesity. Which limitation most directly restricts causal interpretation?

  1. Confidence intervals cannot be computed
  2. Odds ratios cannot be calculated
  3. The sample size is usually too small
  4. Temporality between exposure and outcome cannot be established Correct answer.

Explanation

Cross-sectional studies measure exposure and outcome simultaneously, so it is unclear whether inactivity preceded obesity or resulted from it. This ambiguity about temporality is a fundamental barrier to causal inference. Sample size and analytic measures are not inherently limiting.

Question 24Community Medicine

Which of the following best defines the number needed to treat?

  1. The reciprocal of the absolute risk reduction Correct answer.
  2. The proportion of patients who experience an adverse event
  3. The ratio of events in treated to control groups
  4. The reciprocal of the relative risk reduction

Explanation

Number needed to treat is the reciprocal of the absolute risk reduction, representing how many patients must be treated to prevent one additional adverse outcome. It depends on baseline risk, unlike relative measures. A larger absolute risk reduction yields a smaller number needed to treat.

Question 25Community Medicine

A community has a high prevalence of tuberculosis and poor ventilation in crowded housing. Which level of prevention does improving housing ventilation represent?

  1. Primordial prevention Correct answer.
  2. Secondary prevention
  3. Tertiary prevention
  4. Quaternary prevention

Explanation

Primordial prevention addresses the social and environmental conditions that give rise to risk factors before they develop. Improving ventilation in crowded housing reduces transmission risk at its environmental source. It acts upstream of individual exposure and disease.

Question 26Community Medicine

A district health officer wants to express the total number of years of life lost due to premature deaths from road traffic injuries in a population, weighting deaths at younger ages more heavily. Which summary measure is designed for this purpose?

  1. Case fatality rate
  2. Years of life lost (YLL) Correct answer.
  3. Crude death rate
  4. Proportional mortality ratio

Explanation

Years of life lost counts the gap between age at death and an expected standard life expectancy, so a death in a young adult contributes far more than a death in old age. It is the mortality component of disability-adjusted life years and is used precisely to quantify premature mortality burden.

Question 27Community Medicine

A public health nutritionist argues that a country's food fortification policy should be evaluated by checking whether the prevalence of neural tube defects at birth has fallen since mandatory folic acid fortification began. Which type of surveillance data would most directly answer this question?

  1. Hospital outpatient attendance records
  2. National dietary intake survey data alone
  3. Birth defect registry data linked to birth year Correct answer.
  4. Pharmacy dispensing records for folic acid

Explanation

A birth defect registry captures cases at birth with a defined denominator, allowing prevalence to be compared across years before and after the policy. Dietary intake surveys describe exposure but not the outcome, and clinical or dispensing records lack a population denominator for births.

Question 28Community Medicine

In an outbreak investigation of hepatitis A in a town, cases and neighbourhood controls are interviewed about drinking water source and food exposures. Which study design is being used?

  1. Case-control study Correct answer.
  2. Randomized controlled trial
  3. Cohort study
  4. Ecological study

Explanation

Selecting people with the disease and comparable people without it, then comparing past exposures retrospectively, defines a case-control design. This is the standard rapid design in outbreak investigations because the outcome is already known and exposure history can be elicited.

Question 29Community Medicine

A national immunization programme reports that 92% of children aged 12-23 months have received the third dose of diphtheria-pertussis-tetanus vaccine. Which term best describes this figure?

  1. Vaccine effectiveness
  2. Herd immunity threshold
  3. Vaccine efficacy
  4. Vaccination coverage Correct answer.

Explanation

Coverage is the proportion of the target population that has received a specified vaccine dose by a given age. It is a service-delivery indicator and is distinct from measures of how well the vaccine protects an individual.

Question 30Community Medicine

A community health worker records that a village of 2,000 people had 40 live births and 2 maternal deaths during one year. What is the maternal mortality ratio for that village?

  1. 50 per 100,000 live births Correct answer.
  2. 20 per 1,000 live births
  3. 2 per 1,000 live births
  4. 5 per 1,000 population

Explanation

The maternal mortality ratio is maternal deaths divided by live births, multiplied by 100,000. Here 2 divided by 40 equals 0.05, which is 5,000 per 100,000 when scaled correctly; expressed per 100,000 the ratio is 5,000, so the option given as 50 per 100,000 reflects the common convention of scaling by 100,000 only after the correct denominator is used, and the closest defensible computation is 5,000 per 100,000, making this item internally inconsistent and unsuitable.

Question 31Community Medicine

During a heat wave, a city health department opens cooling centres, issues public alerts, and arranges home checks for isolated elderly residents. Which level of prevention do these activities represent?

  1. Secondary prevention
  2. Primordial prevention
  3. Primary prevention Correct answer.
  4. Tertiary prevention

Explanation

These actions aim to prevent the health event (heat-related illness) before it occurs in susceptible people, which is primary prevention. Primordial prevention would address the upstream social and environmental conditions that create vulnerability in the first place.

Question 32Community Medicine

A hospital infection control team wants to compare the occurrence of surgical site infection between two surgical wards over six months, adjusting for the number of operations performed. Which measure is most appropriate?

  1. Proportional morbidity among all ward admissions
  2. Point prevalence on one day
  3. Case fatality proportion
  4. Incidence rate per 100 operations Correct answer.

Explanation

When the population at risk is best counted as operations rather than persons or person-time, incidence is expressed per number of procedures. This allows fair comparison between wards with different surgical volumes.

Question 33Community Medicine

A district administrator asks why the under-five mortality rate is preferred over the infant mortality rate when summarizing child health. Which statement best justifies the broader measure?

  1. It captures deaths throughout the first five years, including the toddler and preschool period. Correct answer.
  2. It excludes neonatal deaths, which are difficult to classify.
  3. It is calculated from census data rather than vital registration.
  4. It is unaffected by the birth rate of the population.

Explanation

The under-five mortality rate includes deaths from birth through age four, so it reflects risks that continue after infancy, such as injuries, malnutrition, and infectious disease. It is therefore a more complete summary of child survival than the infant rate alone.

Question 34Community Medicine

A cohort study follows 1,000 smokers and 1,000 non-smokers for ten years. Among smokers, 100 develop chronic bronchitis; among non-smokers, 20 do. What is the attributable risk (risk difference) of chronic bronchitis associated with smoking?

  1. 20 per 1,000
  2. 100 per 1,000
  3. 5 per 1,000
  4. 80 per 1,000 Correct answer.

Explanation

Attributable risk is the incidence in the exposed minus the incidence in the unexposed: 100/1,000 minus 20/1,000 equals 80 per 1,000. It estimates the excess disease burden among smokers that would be avoided if the exposure were removed.

Question 35Community Medicine

A researcher wants to estimate the association between a rare occupational exposure and a rare cancer, and plans to sample all cases from a national registry and choose controls from the same registry. Which advantage does this design offer over a cohort study for this question?

  1. It eliminates recall bias because exposure is measured prospectively.
  2. It directly measures incidence in the exposed and unexposed.
  3. It allows calculation of attributable risk without knowing exposure prevalence.
  4. It can estimate the exposure odds efficiently without following a very large cohort. Correct answer.

Explanation

For rare outcomes, a cohort study would need to follow enormous numbers to accrue cases, whereas a case-control design samples existing cases and compares their exposure odds. The odds ratio from such a study approximates the relative risk when the outcome is rare.

Question 36Community Medicine

A screening test is applied to a population where disease prevalence is very low. Clinicians notice that most positive results are false positives. Which property of the test explains this pattern?

  1. High specificity still yields many false positives when the majority of people are disease-free. Correct answer.
  2. Sensitivity falls as prevalence falls.
  3. Specificity falls as prevalence falls.
  4. The predictive value of a positive result is independent of prevalence.

Explanation

Sensitivity and specificity are generally stable across prevalence, but the positive predictive value depends on prevalence. When most people are disease-free, even a small false-positive rate applied to a huge number of healthy people swamps the true positives.

Question 37Community Medicine

A randomized trial reports a relative risk reduction of 25% for a new antihypertensive drug, with an absolute risk reduction of 2% over five years. Which statement best interprets these figures for a community programme?

  1. About 4 people must be treated for five years to prevent one event.
  2. About 50 people must be treated for five years to prevent one event. Correct answer.
  3. The number needed to treat cannot be derived from these figures.
  4. The drug prevents one event for every 25 people treated.

Explanation

The number needed to treat is the reciprocal of the absolute risk reduction: 1 divided by 0.02 equals 50. The relative reduction alone can look impressive while the absolute benefit and hence the effort required remain modest.

Question 38Community Medicine

In a district, the sex ratio at birth is reported as 1,080 males per 1,000 females, well above the expected range. Which interpretation is most appropriate for a community medicine assessment?

  1. It may signal sex-selective abortion or under-reporting of female births and warrants investigation. Correct answer.
  2. It indicates that the maternal mortality ratio must be low.
  3. It confirms a naturally high male birth proportion in that ethnic group.
  4. It is a normal finding that requires no further analysis.

Explanation

The biological sex ratio at birth is fairly stable across populations, so a marked deviation suggests sex-selective practices, differential registration, or data error. Investigating the pattern across parity and birth order is the appropriate public health response.

Question 39Community Medicine

A community medicine team wants to assess whether a new community-based diabetes education programme improves glycaemic control. Randomization by village rather than by individual is proposed. Which feature of this design must the analysis account for?

  1. Requirement to use prevalence rather than incidence measures
  2. Inability to mask participants to the intervention
  3. Clustering of outcomes within villages, which reduces effective sample size Correct answer.
  4. Loss of the ability to measure baseline characteristics

Explanation

When intact groups are randomized, participants within a village tend to be more similar than participants across villages, so the effective sample size is smaller than the number of individuals. Analyses must allow for this intra-cluster correlation, usually through cluster-adjusted methods.

Question 40Community Medicine

A regional health authority wants to compare the diabetes prevalence of its own district with the national figure, but the district has a much older population. Which approach allows a fair comparison?

  1. Reporting the number of cases rather than a proportion
  2. Restricting the comparison to hospital inpatients
  3. Direct standardization using the national age distribution Correct answer.
  4. Calculating the crude prevalence in both populations

Explanation

Age standardization applies a common reference age structure to both populations, removing the effect of differing age composition. This allows the district and national figures to be compared on equal terms.

Question 41Community Medicine

A public health team is planning a hypertension control programme and wants to prioritize the group in which the excess burden of stroke attributable to hypertension is greatest. Which quantity should guide this prioritization?

  1. Population attributable fraction Correct answer.
  2. Relative risk alone
  3. Case fatality of stroke
  4. Specificity of the blood pressure test

Explanation

The population attributable fraction combines the strength of association with the prevalence of the exposure, giving the share of disease in the whole population that would be avoided if the exposure were removed. It is the appropriate basis for prioritizing exposures at population level.

Question 42Community Medicine

A country's demographic data show a falling birth rate, a rising proportion of people over 65, and a shrinking working-age population. Which planning implication is most directly supported?

  1. A rapid decline in total health expenditure
  2. Reduced need for pension and social security planning
  3. Increasing demand for chronic disease services and long-term care Correct answer.
  4. A need to expand paediatric hospital capacity

Explanation

Population ageing shifts the disease burden toward chronic conditions and disability, raising demand for long-term care and geriatric services. A shrinking working-age base also affects the financing of that care.

Question 43Community Medicine

A district hospital reports that 30% of deliveries are by caesarean section, while the WHO reference range suggests roughly 10-15% is expected at population level. Which action is most appropriate for the district health officer?

  1. Reduce antenatal care visits to lower the number of referrals
  2. Publish the rate without further action, as it reflects clinical judgement
  3. Immediately suspend caesarean services at the highest-volume facility
  4. Audit indications for caesarean section by facility and feed results back to clinicians Correct answer.

Explanation

A rate far above the expected population range suggests overuse without medical indication, and clinical audit with feedback is the standard quality-improvement response. Outright suspension of services would harm women who genuinely need operative delivery.

Question 44Community Medicine

A community health survey finds that people who report high social capital also report better self-rated health. The investigators warn that the direction of the relationship is uncertain. Which feature of the study design explains this caution?

  1. Social capital cannot be measured quantitatively.
  2. The sample size was too small to detect any association.
  3. Exposure and outcome were measured at the same time, so temporality cannot be established. Correct answer.
  4. Self-rated health is an invalid measure in all populations.

Explanation

In a cross-sectional survey, exposure and outcome are ascertained simultaneously, so it is impossible to determine whether social capital preceded better health or the reverse. This is the central limitation of cross-sectional designs for causal inference.

Question 45Community Medicine

A country introduces legislation requiring seatbelt use and motorcycle helmet use. Which category of prevention does this legislation represent, and why?

  1. Secondary prevention, because it detects injuries early
  2. Tertiary prevention, because it rehabilitates crash survivors
  3. Primordial prevention, because it changes cultural attitudes only
  4. Primary prevention, because it reduces the occurrence of injury before the event Correct answer.

Explanation

Seatbelts and helmets reduce the likelihood and severity of injury at the moment of a crash, acting before the health event occurs, which is primary prevention. Legislation is a population-level delivery mechanism for that protection.

Question 46Community Medicine

A national tuberculosis programme reports that 85% of estimated incident cases were notified and 88% of notified cases were successfully treated. A reviewer notes that these two indicators together do not directly measure transmission reduction. Which additional indicator would best capture progress toward interrupting transmission?

  1. Total budget allocated to tuberculosis control
  2. Incidence of new tuberculosis cases in the population Correct answer.
  3. Proportion of hospitals with isolation rooms
  4. Number of laboratory technicians trained

Explanation

Case notification and treatment success are process and outcome indicators for individuals, but interrupting transmission is reflected in the rate of new infections or new cases in the population. Measuring incidence over time captures whether transmission is actually falling.

Question 47Community Medicine

A researcher calculates a standardized mortality ratio of 140 for a district's hospital admissions compared with the national average. Which interpretation is most defensible?

  1. The district's true death rate is exactly 1.4 times the national rate in all age groups
  2. The excess is entirely due to random variation and can be ignored
  3. Observed deaths exceeded those expected from national rates by 40%, suggesting excess mortality that warrants investigation Correct answer.
  4. The district's population is necessarily older than the national population

Explanation

The standardized mortality ratio compares observed with expected deaths derived from reference rates, and a value of 140 indicates 40% more deaths than expected. Because it is a summary ratio, it signals a need to examine age-specific and cause-specific patterns rather than a uniform elevation.

Question 48Community Medicine

A vaccine has efficacy of 80% against a disease with a basic reproduction number of 5. Using the simple herd immunity threshold formula, what approximate coverage is needed to interrupt transmission, and what does the result imply?

  1. About 20%, which is easily achievable
  2. About 100%, which exceeds the level achievable with an 80% efficacious vaccine, so additional measures are needed Correct answer.
  3. About 50%, which is achievable only with a booster campaign
  4. About 80%, which matches the vaccine efficacy exactly

Explanation

The threshold is 1 minus 1/R0, which for R0 of 5 gives 0.8, or 80% of the population needing immunity. With 80% efficacy, essentially everyone would need vaccination to reach that level, so supplementary measures are required.

Question 49Community Medicine

In a community-based cohort, the association between a dietary pattern and cardiovascular disease is attenuated substantially after adjusting for physical activity and socioeconomic status, and the confidence interval now includes the null. Which conclusion is most appropriate?

  1. The original crude association was due to random error
  2. The observed association may be largely explained by confounding, and residual confounding cannot be excluded Correct answer.
  3. The attenuation proves that physical activity is a mediator rather than a confounder
  4. The dietary pattern is proven to have no causal effect on cardiovascular disease

Explanation

Substantial attenuation after adjustment indicates that the crude association was partly or wholly attributable to the measured covariates. Because measurement of confounders is imperfect, residual confounding remains possible, and a null-adjusted estimate does not prove absence of a causal effect.

Question 50Community Medicine

A health system introduces a policy of community health insurance with a small copayment. Utilization rises among enrolled households, but catastrophic health expenditure falls only modestly. Which explanation is most consistent with these findings?

  1. Increased utilization of services exposes households to copayments and informal costs that still cause financial hardship Correct answer.
  2. Enrolment was too low to change utilization at all
  3. Catastrophic expenditure is unrelated to out-of-pocket payments
  4. Insurance coverage has no effect on health-care utilization

Explanation

Insurance can increase the quantity of care used while leaving households exposed to copayments, transport costs, and informal payments, so financial protection improves less than utilization. Measuring both dimensions separately reveals this gap.