incidence density
The rate of new psychiatric disorder cases per unit of person-time at risk in a defined population.
Full Definition
Incidence density measures the instantaneous rate at which new cases of psychiatric disorders occur in a population over a specific time period. Unlike cumulative incidence, it accounts for varying periods of observation among study participants and is particularly useful in psychiatric epidemiology where follow-up times may differ significantly. It is calculated as the number of new cases divided by the total person-time at risk, typically expressed per 1,000 or 100,000 person-years. This measure is especially valuable in longitudinal psychiatric studies where participants may enter or leave the study at different times.
Usage
Usage note: Often confused with simple incidence rate; emphasize the person-time denominator when editing.
In Context
- "The incidence density of major depressive disorder was 12.3 per 1,000 person-years in the community sample." — Research paper
- "When calculating incidence density, ensure that person-time at risk excludes periods when participants already had the disorder." — Methods section