Epidemiology & Public Health

Basic

Attack Rate

Proportion of an exposed population that develops the illness during an outbreak.

Formula

AR = \frac{\text{Cases during outbreak}}{\text{Population exposed}} \times 100

Variables

ARAttack rate (%)

\text{Cases during outbreak}People who fell ill

\text{Population exposed}Total people exposed

Example

30 ill at a 120-person event → AR = 25 %

Did You Know?

Food-borne outbreaks are classic attack-rate investigations — the dish with the highest AR among eaters is usually the culprit.

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More in Epidemiology & Public Health

Incidence Rate

Rate at which new cases of a disease appear in a population over a given period.

Prevalence

Proportion of a population that has a particular condition at a point in time.

Basic Reproduction Number

Average number of secondary infections produced by one infected individual in a fully susceptible population.

Herd-Immunity Threshold

Minimum fraction of the population that must be immune to prevent sustained spread.

Effective Reproduction Number

Actual average infections per case when part of the population is already immune.

SIR Model — Susceptible

Rate of change of the susceptible population in the SIR compartmental model.