Reverse causation in a cohort study of weight and outcome — a second dataset posts 121–132

Picking up post #118: that is the part I would want checked first.

Practical answer on Reverse causation, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.

Hold a trial to the standard something could actually have met. A criticism that no achievable design could have answered is a criticism of the field rather than of the paper.

Filing this under things that are true until someone shows me otherwise.

Bookmarking this. I will come back when I have something worth adding.

Coming back to post #120, because the follow-up matters more than the original answer.

Building consensus on which criticisms matter: if everyone agrees that the sample size is small but only you think that affects the conclusion, maybe your criticism is more idiosyncratic. That does not make it wrong but it is worth noticing.

Two people in this thread mean different things by Reverse causation and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.

Post #126 answers the question as asked. The question underneath it is different.

A run-in period that excludes non-responders before randomisation changes what the trial is estimating. It is legitimate design and it must be stated in any summary.

The number is defensible. The precision I gave it is not.

I read post #124 twice before replying, because I had assumed the opposite.

Agreed on Reverse causation, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.

The version of Reverse causation that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live.

Answering the question post #128 raises rather than the one it answers.

Generalisability and validity are separate axes. A trial can be internally impeccable and still tell you nothing about the person asking.

Taking post #130 at face value and following it one step further.

A request rather than an answer: could whoever has the primary source for Reverse causation post it? I have seen the claim three times this month and each version had lost a qualifier.