Generalizability vs. Transportability in Trials

Thank you, Pavlos. The oversimplification point is fair, and I take it on board. The blog format does push toward cleaner narratives than the debate warrants, and I probably underplayed how reasonable the parametric counterargument is in practice.

The RNCT observation is sharp, and I wish I’d included it. You’re right that it’s noted by Matthews but I missed its value as a diagnostic. It cuts through a lot of the abstract framework debate by posing a concrete question: if randomization’s inferential purpose requires a comparison group, what exactly is a randomized non -comparative trial doing? The fact that this design exists, is advocated, and gets published reveals something about how the justification for randomization is being understood, or misunderstood.

My one hesitation about calling it a crystal clear sign is that the motivation behind RNCTs isn’t always straightforwardly inferential confusion. Your linked thread suggests they are often recommended at oncology workshops when there aren’t enough resources to power a comparative trial — randomization retained as a kind of procedural legitimacy device even when comparison is abandoned. That might be a different kind of error: conflating the procedural and inferential roles of randomization, rather than a direct misreading of Fisher. Though perhaps that distinction doesn’t rescue the practice much. If practitioners can’t articulate why they are randomizing when there is no comparison, that itself reflects exactly the misunderstanding of Fisher’s framework you’re describing, and may even strengthen rather than soften your point.

I’ll look more carefully at the RNCT thread; it seems like a natural extension of the series.