Table 1 Definitions of Numerators and Denominators
From: Calculating incidence rates and prevalence proportions: not as simple as it seems
| Â | Numerator | Denominator |
|---|---|---|
Incidence rate | ||
 Incidence rate: person-years | Sum of all new episodes of illness in 2012 | Person-years |
 Incidence rate: person-years at-risk | Sum of all new episodes of illness in 2012 | Person-years at-risk |
 Incidence rate: midterm population | Sum of all new episodes of illness in 2012 | Midterm population |
Prevalence proportion | ||
 Point-prevalence proportion | Episodes on December 31th | Population on December 31th |
 1 year period prevalence proportion | Episodes in 2012 | Person-years |
 Contact prevalence proportion | Number of persons with ≥1 contact in 2012 | Person-years |