The capture-recapture method serves to estimate a quantity (e.g. people with a specific trait) from a population.In epidemiology it is most commonly used to conduct measurements in a population that you cannot count completely.

The technique derives from counting animals, where a certain amount of animals where captured and marked and then released again. After a certain period of time a second sample of the animals were taken. The amount of marked animals in this second sample allows to draw conclusions about the true size of the population.

Certain assumtptions must be met in order to obtain reliable results:

- The population should not change within the two times of capture

- The sources should be independent: i.e. capture by one source should not affect a subject’s likelihood of being captured by another source

- Sufficient information should be available in each source to match subjects from different sources in a unique manner

- Each subject should have an equal likelihood of capture, or certain segments of the population should not be more likely than others to be captured