person-time
A measure combining the number of people in a study with the duration of their observation period.
Full Definition
Person-time (also called person-years when expressed annually) is a fundamental epidemiological concept that accounts for both the number of individuals studied and the length of time each person is observed. In psychiatric epidemiology, person-time is essential for calculating incidence rates and allows for meaningful comparisons between studies with different follow-up periods. For example, following 100 people for 2 years yields 200 person-years of observation. This measure is particularly important in longitudinal studies where participants may enter or leave the study at different times, creating varying observation periods.
Usage
Usage note: Specify units (person-years, person-months) and account for varying observation periods in calculations.
In Context
- "The study accumulated 15,847 person-years of follow-up data across all participants." — cohort study methodology
- "Incidence rates were calculated per 100,000 person-years to standardize across populations." — epidemiological analysis