Propensity score analysis

• Statistical methods used to control for treatment selection bias in observational studies
• Propensity score is the probability of treatment assignment conditional on observed baseline characteristics
• A propensity score allows one to conduct an observational study in such a way that it might mimic some of the characteristics of a randomised controlled trial
• This is good - observational studies cannot rely on randomisation to correct for confounding factors
• If a group of subjects have the same propensity score, they should all have the same baseline characteristics.
• Thus, propensity score analysis can compare subjects with similar propensity scores, thus attempting to negate the presence of confounding factors

Advantages

• Running an observational study with propensity score analysis is cheaper and easier than running an RCT
• This is a way of studying treatments which cannot be ethically randomised

Disadvantages

• This is a statistical method, so it can only demonstrate an association, not causation
• Propensity analysis assumes that all possible confounding variables have been measured in the observed population (but of course they have not)
• Nobody can agree which confounding variables to measure, and when
• One can include all sorts of meaningless variables, which add complexity without adding any validity