Measures of Morbidity: Incidence Rate and Attack Rate

Numerator

The numerator is the number of new cases in a particular population during a specified time period.

How does one identify all new cases in a population during a specified time period? There are two possible approaches:

  1. Monitor the entire population repeatedly over time
  2. Screen the entire population for diseaseà follow those without disease for a specified time periodà rescreen for diseaseà identify new cases, follow up non-diseased for specified time periodàrescreen for disease….

In the second approach, any cases diagnosed from those previously non-diseased at initial screening, must be new cases.

Numerators alone are not very informative, as the denominator is required to see the numerator in perspective. However, if the denominator is stable over time, one may be able to draw useful information from a scrutiny of the numerator alone. For all practical purposes, however, both numerator and denominator must be available to make valid comparisons.

2 thoughts on “Measures of Morbidity: Incidence Rate and Attack Rate

  1. Pingback: Measures of Morbidity: Prevalence | communitymedicine4all

  2. Pingback: Risk ratio versus Rate ratio | communitymedicine4all

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.