Discussion of research using propensity‐score matching: Comments on ‘A critical appraisal of propensity‐score matching in the medical literature between 1996 and 2003’ by Peter Austin, Statistics in Medicine

Research using propensity-score matching has been in the literature for over two decades now. During this time, in a process akin to the way a message gets distorted and passed on in the children’s game of ‘telephone,’ widespread dissemination has led to misunderstandings regarding the required assumptions, goals, and appropriate implementation of propensity-score matching. Thus, the bad practice that exists today is due, in large part, to degrees of separation from original sources coupled with the changing knowledge base and the time lag between new information appearing in the statistics literature and it reaching applied researchers. Another culprit more intrinsic to the nature of the method itself (at least in its current incarnation) is the ‘art form’ involved in proper practice [1]. Irrespective of how the current state of affairs came to be, a remedy is warranted. Peter Austin should be commended for addressing the rampant lack of good practice in propensity-score matching applications with some much needed policing and rehabilitation. Austin provides some useful advice with regard to good practice (I avoid the term ‘best practice’ since there seems to be no consensus as to what this comprises). I especially appreciate his push for explicit discussion of the strategy used to create matched pairs and examination of balance across matched groups. Austin also provides advice with which I don’t agree. I am particularly at odds with his position requiring matched pairs’ analyses, which is an overly narrow approach to the problem. There are many ways to address the lack of independence across samples, and methods that explicitly adjust for pairwise dependence are not always the best choice (even if, algorithmically, the dependence was created by forming matched pairs). Moreover, Austin gives this issue undue weight compared