Propensity Score Matching

What is PSM

• Propensity score = the probability of each participant being in the group A or B
  • e.g. group A is with treatment, group B is without treatment
• Propensity Score Matching (PSM) is a quasi-experimental method the researcher uses statistical techniques to construct an artificial control group by matching each treated unit with a non-treated unit of similar characteristics
• Using these matches, the researcher can estimate the impact of an intervention

How does it work

It is basically a logistic regression using the control covariates

• calculate the propensity score of
  • the disease/treatment group based on the control variables
  • the control group based on the control variables
• match individuals from the control group to those in the disease group with similar scores using K-Nearest Neighbor

Why PSM is useful

• it can help create matched groups
• it can help avoid confounds: Causal inference#Confounds in causal inference
• it can provide robust solution for estimating causal effects in observational studies