Collider in RCT Subgroup Analysis

I don’t follow. Do you mean b to be a subgroup variable acting as an effect modifier or a subgroup variable being post-randomization or treatment-associated?

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with RECOVERY but the authors went with b) and all I am saying is that b) just represents overfitting because there is no clear indication in my mind that ventilation status represents a variable associated with dexamethasone in a post-randomization sense