Causal estimates for external controls. How reasonable are the assumptions?

Abstract A causal model has been proposed for including external controls in randomized clinical trials that is based on five critical assumptions and has been illustrated using the example of two trials in spinal muscular atrophy. It is argued that four of these assumptions are obviously false in the example used and that this would be a problem for many cases where one sought to use the approach. The claimed superiority to Bayesian methods is debatable, since trial effects have not been allowed for. It is concluded that trialists should be cautious in applying such an approach to using external controls.