[Propensity Score Methods to Estimate Treatment Effects: An Opportunity for Rehabilitation Service Research].

The randomized controlled trial is the gold standard to validate the efficacy of an intervention. Randomized treatment assignment in intervention and control group independent of patient characteristics or previous measures of patient care allows one to estimate unbiased treatment effects. Differences in outcomes can be attributed causally to the treatment. In observational studies treatment assignment is not randomized in intervention and control group. Instead, the assignment is influenced by patient characteristics. This could lead to biased estimates of treatment effects. Statistical approaches based on the propensity score take into account the group differences in observational data. The propensity score is the probability of treatment assignment conditional on observed variables. By means of propensity-score-matching balanced samples of treated and control subjects can be formed. To express treatment effects, the same statistical approaches can be used as those in randomized controlled trials.