Example: Person-Time Incidence - Pediatric Cardiomyopathy

Lead Author(s): Jeff Martin, MD

Study of Pediatric Cardiomyopathy

Lipshultz 2003 Study presents:


Numerators: Based on patients who received a diagnosis of cardiopathy between 1996 - 1999


Denominator: Population estimates (incidence-rate denominators) are taken from the 1990 U.S. Census,

Annual Incidence

Overall annual incidence: 1.13 per 100,000 children Calculating annual rates is a common practice as many statistics are gathered annually. The way these rates are often reported might lead you to think they are proportions as they are frequently described as per some number of persons without making explicit that it is really per some number of person-years.

Reporting Cancer Rates

The choice of the person-time denominator is usually determined by a desire to have at least one integer to the left of the decimal point. So events that are relatively rare, such as the example of pediatric cardiomyopathy above, are often reported per 100,000 person-years. For the same reason cancer rates are usually reported per 100,000 person-years.


Lipshultz, S. E., Sleeper, L. A., Towbin, J. A., Lowe, A. M., Orav, E. J., Cox, G. F., et al. (2003). The incidence of pediatric cardiomyopathy in two regions of the United States. N Engl J Med, 348(17), 1647-1655.