Annual Proportion of An Incident Cohort Progressing Under An Exponential Distribution. In this example, an incident cohort at year 0 progresses to a subsequent health state at an annual rate of 0.078, corresponding to a constant annual risk of 7.5%. This results in 7.5% (1*.075) of the original cohort progressing in year 1. By the start of year 10, 49.6% of the original cohort remains in the initial health state, and only 3.7% (.496*.075) progress during year 10. Regardless of the value for risk chosen, the absolute proportion progressing will be highest during year 1 and decline steadily with time. For simplicity, mortality and disease regression are not modeled here.
Insinga et al. BMC Infectious Diseases 2009 9:119 doi:10.1186/1471-2334-9-119