Free FMGE Community Medicine (PSM) questions

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Incidence measures new disease occurrence among persons initially at risk. It is especially useful for studying disease causation and risk.

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Prevalence is influenced by both disease incidence and duration. Longer survival with persistent disease increases the number of existing cases at a given time.

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Case-control studies begin with diseased and non-diseased groups, so disease incidence cannot usually be calculated directly. The odds ratio is the standard measure of association.

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Cohort studies measure disease incidence in exposed and unexposed groups. Their ratio provides the relative risk.

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Sensitivity equals true positives divided by all individuals who truly have the disease. A highly sensitive test minimizes false negatives.

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Specificity equals true negatives divided by all individuals without disease. Highly specific tests generate relatively few false positives.

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Positive predictive value depends strongly on pretest probability or prevalence. As prevalence increases, a positive result is more likely to represent true disease.

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Screening can move the time of diagnosis earlier without changing the course of disease. Survival measured from diagnosis then appears longer even when death occurs at the same time.

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Randomization reduces systematic differences between intervention groups and helps balance confounding factors. It strengthens causal inference when properly implemented.

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Systematic sampling selects units at a fixed interval after a random start. It is simple and efficient when an appropriate sampling frame is available.

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The median depends on the ordered position of observations rather than their magnitude. It is therefore relatively resistant to extreme outliers.

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Standard deviation quantifies dispersion of values around the mean. A larger standard deviation indicates greater variability in the distribution.

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When a sufficiently large proportion of a population is immune, chains of transmission are interrupted. This indirectly lowers exposure risk for susceptible individuals.

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Secondary attack rate measures the occurrence of disease among susceptible contacts exposed to primary cases within a defined setting and incubation period.

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Many diseases have a substantial hidden component consisting of mild, subclinical, carrier, or unrecognized cases. The clinically apparent cases form only the visible tip.

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Primordial prevention acts before conventional risk factors become established. It targets social, environmental, and behavioral conditions that promote future disease risk.

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Adsorbed vaccines containing aluminum salts, including pentavalent vaccine, can be damaged by freezing. Freeze damage may cause irreversible loss of potency.

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Vitamin A deficiency causes ocular manifestations including conjunctival xerosis, Bitot spots, and more advanced xerophthalmia. It is an important preventable cause of visual morbidity.

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During chlorination, added chlorine is initially consumed by reducing substances and combined forms. Beyond the breakpoint, further addition produces free residual chlorine available for disinfection.

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Byssinosis is associated with inhalation of cotton, flax, or hemp dust. Symptoms may be characteristically prominent after a period away from exposure.