Epidemiological investigations often involve the use of retrospective, or case-control studies, where a person known to have the event of interest (case) is paired, or matched, with a person who doesn’t have the event (control). The idea is to determine whether the exposure factor is associated with the event; this is presumably made less complicated by using matching to control for possible covariates.
In a 1:1 matched study, the matched set consists of one case and one control from each stratum. This is the most common situation.
In a 1:m matched study, the matched set consists of one case and m controls. Usually, m ranges between 2 and 5.
In the m:n matched study, the matched set consists ...