It expresses the number of deaths in a population relative to its size, over a specific time period.

This is known as the mortality rate. It is typically calculated by taking the number of deaths in a population, dividing it by the total population, and then multiplying the result by a specific number (usually 1,000 or 100,000) to get a rate per thousand or hundred thousand. This rate is then often expressed per year, or another set time period.

Here are the steps:

1. Count the number of deaths in the population over the specific time period.
2. Divide this number by the total population size.
3. Multiply the result by 1,000 or 100,000 (depending on whether you want the rate per thousand or per hundred thousand).
4. The result is the mortality rate per thousand or hundred thousand for the specific time period.