8.1 Basics

“broadly […] any method that aims to equate (or "balance") the distribution of covariates in the treated and control groups” (Stuart 2010, 2)
Goal:
- “for every treated unit, to find one (or more) non-treated unit(s) with similar observable characteristics against whom the effect of the treatment can be assessed” (Wikipedia contributors 2016)
- Treatment and control group as similar as possible except for the treatment status (Balance!)
Approach
- Exclude/prune (or down-weight) observations without comparable units in both treatment and control
Q: What tradeoff is there when it comes to pruning units (think of representativeness)?

Stuart, E A. 2010. “Matching Methods for Causal Inference: A Review and a Look Forward.” Stat. Sci.