Assessment of Matching Methods for Causal Analysis

Matching is commonly used in comparative observational studies where research subjects cannot be randomly assigned to comparison groups.
There are circumstances in which randomization is not a practical nor ethical way to assign subjects to groups being compared. For example, we cannot assign patients to smoke or not to evaluate the impact of smoking on lung function. In such circumstances, matching is used to reduce bias.
It is used more often in case-control studies than in cohort studies.
It is also used in clinical trials
Matching is very important in increasing the efficiency of a study (Faresjo & Faresjo, 2010).