Are Target Trial Emulations the Gold Standard for Observational Studies?

There has been considerable debate in epidemiology about whether the randomized controlled trial (RCT) is the gold standard for epidemiologic studies; some of the debate is old, but some is new. Almost all are agreed that a well-conducted RCT, where possible and appropriate, is to be preferred because an experimental set-up enables control of several key features of a study, and randomization ensures that, on the average, and provided that there are no other biases (e.g., in the ascertainment of the outcome), that the groups being compared are comparable (exchangeable) with regards to baseline (i.e., in the absence of exposure) outcome risk. It is thus tempting to apply the RCT paradigm to observational studies, that is, to propose that if an RCT is not possible for a particular issue, then an observational study that closely mimics the RCT approach is the most preferable.