Person-years is a term researchers use to describe how often new cases of a disease (e.g. diabetes) or medical event (e.g. anaphylaxis) occur over a specified period for a defined, at-risk population. A risk quoted as 5 cases of diabetes per 100 person‐years, for example, means that you could expect 5 new cases of diabetes among 100 people at risk of developing diabetes if you observed them for 1 year, or among 50 such people observed for 2 years, or 10 such people observed for 10 years, etc. A more detailed calculation example can be found here.
