Increasing availability of large clinical data sets is driving a proliferation of observational epidemiology studies in perioperative care. This wealth of data must be judged both on its inherent quality and the statistical techniques used to analyse the data set. Without some basic understanding of the methods involved, it remains difficult to interpret the results of these perioperative studies. Indeed, some studies' conclusions may be very persuasive, but their limitations may necessitate cautious interpretation. In this editorial, we will briefly describe the statistical technique of propensity scoring, identifying when propensity scoring methods should be used and practical considerations in the development and the application of propensity scoring methods. We will conclude with some comments on the strengths and limitations of propensity scoring methods.