What is matching? What is the procedure about?

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Thank you.

Matching is a statistical procedure to evaluate the effect of a treatment by comparing the treated and the non-treated units in an observational study or quasi-experiment (i.e., when the treatment is not randomly assigned). Matching reduces bias due to confounding and enables a comparison of outcomes among treated and non-treated units to estimate the effect of the treatment. Generally, you must identify the potential confounders first. The second step is to decide and apply the matching strategy, either by a comprehensive score integrating all the confounders (e.g., propensity scores) or by matching on each confounder respectively. The third step is to assess the success of the matching with balance diagnostics, graphically or analytically. The fourth step is to apply appropriate statistical methodology using the matched data to compare outcomes among treatment groups.