Every mortality rate is deaths over a population, times a base
The four measures differ only in which deaths go on top, which population goes on the bottom, and the base you scale by. Pick the base so the result reads as a whole number.
The four measures side by side
| Measure | Numerator | Denominator | Usual base |
|---|---|---|---|
| Crude mortality rate (CMR) | All deaths | Mid-year population | per 1,000 |
| Cause-specific rate | Deaths from one cause | Mid-year population | per 100,000 |
| Case fatality rate (CFR) | Deaths from a disease | Cases of that disease | per 100 (i.e. %) |
| Infant mortality rate (IMR) | Deaths under age 1 | Live births | per 1,000 |
The CFR denominator is diagnosed cases, not the whole population, so it answers "how deadly is this disease" rather than "how common is death here."
Roughly where these numbers land
- Crude rate. Around 7 to 8 per 1,000 globally; typically 7 to 11 in wealthy countries, higher where the population skews older or poorer.
- Infant rate. Below 4 per 1,000 births in the lowest countries; 40 or more in the poorest regions.
- Case fatality. A percentage, capped at 100%. It swings with testing and care, so the same disease can read very differently between places.
The crude rate misleads when populations differ in age
A country full of older people posts a higher crude rate even when its actual risk at each age is lower. To compare places fairly, apply each group's rate to one standard age structure. That is the age-adjusted rate.
Identical risk at every age, but the crude rate looks worse purely because the population is older. Age-adjusting removes that distortion.
Common questions
How do you calculate a mortality rate?
Divide deaths by the population at risk, then multiply by a base. The crude rate uses deaths divided by mid-year population times 1,000. So 8,000 deaths in a population of 1,000,000 is 8 per 1,000.
What is the difference between the mortality rate and the case fatality rate?
The mortality rate divides deaths by the whole population, measuring how common death is overall. The case fatality rate divides deaths by the number of people who had a specific disease, measuring how deadly that disease is once caught.
Why is per 1,000 used for some rates and per 100,000 for others?
The base is chosen so the number reads cleanly. Common events like all-cause and infant deaths use per 1,000; rarer, cause-specific deaths use per 100,000 so the figure is not a tiny fraction.
