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  "path": "/t/collider-in-rct-subgroup-analysis/28689?page=2#post_26",
  "publishedAt": "2026-05-20T04:24:59.000Z",
  "site": "https://discourse.datamethods.org",
  "tags": [
    "Zenodo",
    "A new structural analysis of randomized trials: three estimands for trial..."
  ],
  "textContent": "Let’s start with the key issue which is: what defines a CIR versus a CAR/SDGP design?\n\nI agree that randomization preserves exchangeability within the oxygen strata and therefore supports internal causal identification within the trial. But from my perspective, exchangeability alone is not sufficient to define a CIR.\n\nA CIR is not defined merely by successful randomization.It is defined by whether the enrollment gate selects a coherent biological data-generating process such that the trial estimand is E2 and corresponds to a functionally causal system rather than a synthetic mixture. This is also true of the subgroup.\n\nIn other words, the defining question is what kind of causal system (S=1) actually represents at the main gate and (S=1)* at the subgroup gate.\n\nFirst we look at the main gate and it’s one disease, a valid BDGP.\n\nSecond we look at the subgroup gate and it’s a proxy for an enrichment phenotype that, while not pure, is strongly supported by respiratory pathophysiology.\n\nIn that framework, the control arm serves as the counterfactual for the treated arm within each oxygen category.\n\nConversely, if the gate is a SDGP such as the ARDS criteria, that primarily aggregates a mixture diseases and divergent treatment-response mechanisms, or the subgroup gate is a SDGP then the trial shifts toward a CAR/SDGP structure even if the randomized comparison itself remains internally valid. The primary gate was an SDGP for the COVID ventilator guidelines which failed and have been abandoned.\n\nWhen the gate is an SDGP (that is not rescued by a narrowing coherent physiologic target in substantially all the participants), the estimand has moved to layer three (E3) and is dependent on the instant mixture of causal systems.\n\nSo for me the central issue is not whether randomization solved a mediator problem, but whether the main gate and subgroup gate selected a coherent causal system capable of generating transportable biologic knowledge.\n\nThis is a preprint in review. Note it does not address subgroups. Your presentation has made me realize that the CIR to CAR conversion can occur at the subgroup level even if the main gate (S=1) was an acceptable BDGP. but it is my argument that the RECOVERY design remained a solid Fisher//Hill CIR and grade A evidence.\n\nZenodo\n\n### A new structural analysis of randomized trials: three estimands for trial...\n\nThis article presents a new conceptual and methodological analysis of the transportability of randomized trial estimates under different enrollment structures. Building on prior structural work contrasting cause agnostic randomized controlled trials...",
  "title": "Collider in RCT Subgroup Analysis"
}