Definition: The ratio of the number of deaths caused by a specified disease to the number of diagnosed cases of that disease. Another way to say this is the proportion of people who will die of a certain disease out of those who contract it. This rate can be impacted by the number of mild cases not reported.

Example: For acute infection, like measles, a time limit from the onset of the illness is needed. So the case fatality rate for measles is often measured as those who die within 4-6 weeks after the rash appears.