Where I part company with post #4, and it is a narrow parting. Double extraction with disagreement resolution is standard and is worth checking for, because single extraction errors are common and non-random. Worth checking against a second source before it gets quoted onward.
The question in the title: What pooling buys you and what it destroys I will give what I have already checked below so nobody repeats it.
The question about pooling buys that I actually want answered is the second one below. The first is context and I have kept it short.
Both are stated with units, and I have said what I already checked so that nobody repeats it.
Confirming the opening post from a second method, which matters more than confirming it from a second person.
What I would want before treating pooling buys as settled: the method, the sample, and whether anyone tried to find the opposite result. Two of the three are usually missing.
That matches what I have seen, for whatever a single anecdote is worth.
Where I part company with post #4, and it is a narrow parting.
Double extraction with disagreement resolution is standard and is worth checking for, because single extraction errors are common and non-random.
Worth checking against a second source before it gets quoted onward.
Post #4 is the version of this I will quote in future. One addition.
Individual participant data pooling is a much stronger design than aggregate pooling and is rare because it requires cooperation rather than a search.
That is my reading. Someone else read the same page differently and was reasonable.
I would put moderate confidence on the mainstream reading of pooling buys and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.
The question underneath pooling buys is usually "how would I tell?" rather than "what is true?", and that one has a method attached to it.
Write down what you would expect to see under each hypothesis before you collect anything. If they predict the same observation, collecting it will not help.
Post #7 put the caveat in the right place and I want to underline it.
Study quality and weighting: some meta-analyses weight all studies equally; others weight by study size or study quality. The choice affects the result and should be stated and justified.
Worth separating pooling buys as a question about the compound from pooling buys as a question about the documentation. They get answered by different people and only one of them is answerable here.
Source for the pooling buys figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.
Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.
Post #11 is the version of this I will quote in future. One addition.
Where the included trials share a sponsor and a protocol template, their errors correlate and pooling does not average them out.
The honest answer is that it depends, and here is what it depends on.
Double extraction with disagreement resolution is standard and is worth checking for, because single extraction errors are common and non-random.
Building on post #16 rather than restating it.
Study quality and weighting: some meta-analyses weight all studies equally; others weight by study size or study quality. The choice affects the result and should be stated and justified.
That is what I would do. It may not be what is correct.
Post #14 put the caveat in the right place and I want to underline it.
Pooling buys is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.
Reading rather than answering, but this is the post I would point somebody at.
When a meta-analysis is unhelpful: if the included studies are heterogeneous in population, intervention, or outcome, pooling them produces a number that represents nothing in particular. Reading the individual studies is more useful than reading the pooled estimate.
I had written a reply contradicting post #20 and deleted it. Here is what survived.
Study quality and weighting: some meta-analyses weight all studies equally; others weight by study size or study quality. The choice affects the result and should be stated and justified.
Scoping that to what I have actually seen rather than what I have read.
Confirming post #23 from a second method, which matters more than confirming it from a second person.
If someone has run pooling buys properly I would rather read that than my own reconstruction of it. Posting mine only because the thread has gone quiet.
Answering the question post #23 raises rather than the one it answers.
Double extraction with disagreement resolution is standard and is worth checking for, because single extraction errors are common and non-random.
Taking pooling buys seriously for a moment rather than deflecting: the honest position is that the community has observations and no controlled comparison, and those two things support very different sentences.
The reason pooling buys keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.
Post #27 is the version of this I will quote in future. One addition.
Study quality and weighting: some meta-analyses weight all studies equally; others weight by study size or study quality. The choice affects the result and should be stated and justified.
It reads as pedantry until the day it does not.
I would call the community position on pooling buys likely rather than established, and I would be comfortable defending that hedge.
Narrowing post #27, because the general version has more than one answer.
Double extraction with disagreement resolution is standard and is worth checking for, because single extraction errors are common and non-random.
The short answer was in the first line; everything after is the working.