Epidemiology & Public Health

Basic

Incidence Rate

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

Formula

IR = \frac{\text{New Cases}}{\text{Population at Risk}} \times k

Variables

IRIncidence rate

\text{New Cases}Number of new cases in the period

\text{Population at Risk}People susceptible to the disease

kMultiplier (e.g. 1 000 or 100 000)

Example

200 new cases in 50 000 at risk → IR = 400 per 100 000

Did You Know?

Incidence tells you the speed at which a disease is spreading — prevalence tells you how much of it already exists.

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More in Epidemiology & Public Health

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.

SIR Model — Infected

Rate of change of the infected population — new infections minus recoveries.