NEET-PG PSM (Community Medicine) Previous Year Questions (2017–2026)

Correct answer: 0.9 (an attributable fraction of 90 percent).

Incidence in the exposed (Ie) = 0.01 and in the unexposed (Iu) = 0.001. The attributable risk (risk difference) = Ie - Iu = 0.009. The attributable fraction in the exposed = (Ie - Iu) / Ie = 0.009 / 0.01 = 0.9, i.e. 90 percent of chronic liver disease among drinkers is due to alcohol. (The absolute risk difference 0.009 was not offered, so the fraction 0.9 is the intended answer.)

Incorrect Options:

• 0.01: 0.01 is only the incidence in drinkers, not the attributable fraction.
  0.01 is only the incidence in drinkers, not the attributable fraction.
• 0.09: 0.09 does not correspond to any step of the calculation.
  0.09 does not correspond to any step of the calculation.
• 0.1: 0.1 is a distractor value.
  0.1 is a distractor value.

High-Yield Facts:

• Attributable risk (risk difference) = incidence in exposed minus incidence in unexposed.
• Attributable fraction in the exposed = (Ie - Iu) / Ie, expressed as a proportion or percentage.
• Population attributable risk uses the incidence in the whole population instead of the exposed.
• A high attributable fraction implies a large preventable burden if the exposure is removed.

Correct answer: 5 percent.

The case fatality rate (CFR) = (deaths due to the disease / number of diagnosed cases) x 100. Here CFR = (10 / 200) x 100 = 5 percent. The CFR measures the killing power of a disease and is applied to acute, short-duration illnesses. The total population, births and other deaths are distractors and do not enter this calculation.

Incorrect Options:

• 1%: 1 percent underestimates deaths among the diagnosed cases.
  1 percent underestimates deaths among the diagnosed cases.
• 10%: 10 percent wrongly uses a denominator other than the number of cases.
  10 percent wrongly uses a denominator other than the number of cases.
• 20%: 20 percent would need 40 deaths among 200 cases.
  20 percent would need 40 deaths among 200 cases.

High-Yield Facts:

• Case fatality rate = (deaths from the disease / diagnosed cases) x 100.
• CFR reflects the virulence or killing power of an acute disease.
• CFR uses cases (not the whole population) as the denominator - do not confuse it with mortality rate.
• Mortality rate uses the total mid-year population as the denominator.

Correct answer: Ecological study.

When the unit of analysis is the population (group) rather than the individual - here whole countries compared using aggregate published data - the design is an ecological (correlational) study. It is cheap and useful for generating hypotheses, but is vulnerable to the ecological fallacy: associations seen at the group level may not hold for individuals.

Incorrect Options:

• Cross-sectional survey: Cross-sectional: exposure and outcome measured in individuals at one time point.
  Cross-sectional: exposure and outcome measured in individuals at one time point.
• Case-control study: Case-control: starts from diseased and non-diseased individuals, looks back at exposure.
  Case-control: starts from diseased and non-diseased individuals, looks back at exposure.
• Cohort study: Cohort: follows exposed and unexposed individuals forward for outcomes.
  Cohort: follows exposed and unexposed individuals forward for outcomes.

High-Yield Facts:

• Ecological studies use the population, not the individual, as the unit of analysis.
• They are quick, cheap and hypothesis-generating, often using existing aggregate data.
• Their main weakness is the ecological fallacy - group-level associations may not apply to individuals.
• Analytical designs (case-control, cohort) use the individual as the unit of analysis.