Propensity-score analysis in thoracic surgery: When, why, and an introduction to how.

Propensity score matching is a valuable tool for dealing with observational data and nonrandom treatment assignment, which often results in groups that differ systematically in numerous measured and unmeasured variables. When these systematically different variables are associated with both group assignment and the outcome(s) of interest, bias is introduced. Propensity score matching assigns a propensity for group assignment, which is then used to create 2 groups that are balanced across all possible variables that might influence exposure assignment. When used in the proper conditions, these analytics allow for more accurate and precise estimates of risk for a variety of outcomes.