incidence rate

Syllable breakdown

Dictionary meaning

a measure of the rate at which new cases of a disease or health event occur in a population at risk during a specified time period, calculated as the number of new cases divided by the person-time at risk — typically expressed as cases per 100,000 person-years; incidence rate captures the dynamic of disease occurrence over time, unlike prevalence which measures the proportion of cases at a single point; incidence rate is the fundamental measure for understanding disease causation, because it quantifies the speed at which susceptible individuals develop disease, and is most informative for acute conditions with relatively short duration; in cohort studies comparing exposed to unexposed groups, the ratio of incidence rates — the incidence rate ratio — provides a measure of the association between exposure and disease; accurate estimation requires careful definition of the population at risk, the time period, and the case definition

Examples

• The incidence rate of tuberculosis in the study population was 45 per 100,000 person-years, declining from 80 per 100,000 a decade earlier.
• Comparing incidence rates between vaccinated and unvaccinated cohorts revealed a 70 percent reduction in disease risk.