PGIM MD Community Medicine key terms

The proportion of people exposed to an infectious agent in a defined group who become ill during a limited period, usually an outbreak. It is a measure of incidence in a closed or well-defined population.

The proportion of susceptible close contacts of a primary case who become ill within the incubation period after exposure. It estimates person-to-person spread and is expressed per susceptible contact, not per whole population.

The proportion of diagnosed cases of a disease who die from it within a stated period. It reflects severity of illness rather than the risk of dying in the whole population.

The time between exposure to an infectious agent and the appearance of the first symptom or sign. It is used to define surveillance windows, contact tracing periods, and periods of quarantine.

The time between onset of symptoms in a primary case and onset in a person infected by that case. It helps estimate epidemic growth and informs how long transmission chains may persist.

The average number of secondary infections produced by one infectious case introduced into a fully susceptible population. A value above one indicates conditions for sustained transmission without control measures.

The proportion of a population that must be immune to interrupt sustained transmission of an infection. It rises with the basic reproduction number and is estimated as one minus one divided by R0.

The probability that a test correctly identifies a person who truly has the condition, expressed as true positives divided by all people with disease. High sensitivity supports ruling out disease when the test is negative.

The probability that a test correctly identifies a person who does not have the condition, expressed as true negatives divided by all people without disease. High specificity supports ruling in disease when the test is positive.

The probability that a person with a positive test result actually has the disease. Unlike sensitivity, it depends on the prevalence of the condition in the population tested.

The probability that a person with a negative test result genuinely does not have the disease. It falls as prevalence rises and is therefore specific to the setting where the test is used.

The presumptive identification of unrecognised disease in apparently healthy people using tests applied rapidly. It is justified only when the condition is important, detectable early, and treatable, with acceptable test performance.

Apparent improvement in survival produced solely by earlier diagnosis, which lengthens the measured time from diagnosis to death without postponing death. It can make screening look beneficial when it is not.

The tendency of screening to detect disproportionately more slowly progressing cases, because such cases remain detectable for longer. Survival appears better in screened groups even if screening changes nothing.

A distortion arising when the groups compared differ systematically in characteristics that affect the outcome, often because of how participants were chosen or retained. It threatens the internal validity of a study.

Distortion of an exposure-outcome association by a third factor that is associated with both the exposure and the outcome but is not on the causal pathway. It must be addressed in design or analysis.

A genuine difference in the magnitude or direction of an exposure's effect across levels of another variable. Unlike confounding, it is a biological or social phenomenon to be reported, not removed.

The ratio of the incidence of an outcome in the exposed group to the incidence in the unexposed group. It is the preferred measure of association in cohort studies and indicates how many times risk is multiplied.

The ratio of the odds of exposure among cases to the odds of exposure among controls. It approximates relative risk when the outcome is rare and is the standard measure in case-control studies.

The difference in incidence between exposed and unexposed groups, representing the excess risk due to exposure. It indicates the absolute number of cases that could be prevented by removing the exposure.

The proportion of all cases in a population that would be avoided if a risk factor were eliminated, assuming causality. It combines the strength of association with how common the exposure is.

An experiment in which participants are allocated by chance to intervention or control groups. Randomisation balances known and unknown confounders, making it the strongest design for causal inference.

Analysis in which participants are compared according to the group to which they were randomised, regardless of adherence. It preserves randomisation and gives an unbiased estimate of the effect of offering the intervention.

An observational design comparing people with a disease to suitable controls without it, then looking back at past exposures. It is efficient for rare outcomes but vulnerable to recall and selection bias.

An observational design following groups defined by exposure status over time to compare incidence of outcomes. It allows direct calculation of incidence and relative risk but may require long follow-up.

Systematic error in which people with a condition remember or report past exposures differently from those without it. It is a particular threat in retrospective case-control designs.

The number of live births in a year per 1,000 people in the mid-year population. It is simple to compute but ignores the age and sex structure of the population.

The average number of children a woman would bear over her lifetime if current age-specific fertility rates persisted. It summarises fertility independently of population age structure.

The fertility level at which a population exactly replaces itself from one generation to the next, commonly about 2.1 births per woman where mortality is low. Sustained below this level leads to population ageing and decline.

The historical shift from high birth and death rates through a phase of rapid growth to low birth and death rates. It explains population ageing and changing disease burdens in many countries.

The shift in a population's disease pattern from infectious diseases and malnutrition towards chronic noncommunicable diseases and injuries, usually accompanying economic and demographic change. It reshapes health service priorities.

The average number of years a newborn would live if current age-specific death rates remained unchanged. It is a summary indicator of overall population health and mortality conditions.

The probability that a child born in a given year dies before reaching age five, expressed per 1,000 live births. It is a sensitive indicator of child health and socioeconomic conditions.

The number of deaths of children under one year of age per 1,000 live births in a year. It reflects maternal and newborn care, nutrition, and environmental conditions.

The number of deaths in the first 28 completed days of life per 1,000 live births. It mainly reflects quality of delivery and newborn care rather than later environmental factors.

The number of maternal deaths during pregnancy, childbirth, or within 42 days of termination per 100,000 live births. It indicates access to and quality of obstetric care.

A summary measure of population health loss combining years lived with disability and years of life lost to premature death. One unit represents one lost year of healthy life.

The number of years of expected life lost because of death occurring earlier than the standard life expectancy. It weights causes that kill young people more heavily than those affecting the elderly.