I had written a reply contradicting the opening post and deleted it. Here is what survived. What I want from this pooling buys thread is the list of things that would need to be true for the claim to hold. If we can write that list, we can check it.
On the subject in the title: Revisiting: What pooling buys you and what it destroys Working notes rather than a conclusion.
Pooling buys — I have the observation and I do not trust my interpretation of it, so I am posting the observation and holding the interpretation back.
Numbers, method and the conditions under which they were collected are below. Interpret them however they warrant.
Confirming post #2 from a second method, which matters more than confirming it from a second person.
Double extraction with disagreement resolution is standard and is worth checking for, because single extraction errors are common and non-random.
One more caveat and then I will stop qualifying: the sample selected itself.
I had written a reply contradicting the opening post and deleted it. Here is what survived.
What I want from this pooling buys thread is the list of things that would need to be true for the claim to hold. If we can write that list, we can check it.
The arithmetic in post #2 is right; the assumption feeding it is the part to check.
On pooling buys, I would rather understate and be corrected upward than overstate and be quoted. That is a house style here and it is a good one.
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.
The variance between people here is larger than the effect being discussed.
Nothing to add on the substance. Thank you for taking the question at face value.
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.
Narrowing post #6, because the general version has more than one answer.
Filing a mild objection to the consensus on pooling buys. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit.
Everything in post #8 holds. The case it does not cover is the one I have.
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.
A weak preference rather than a position.
What I would tell a new member reading about pooling buys for the first time: the confident posts are not the reliable ones, and the reliable ones are longer.
This follows post #11 rather than contradicting it.
The strongest argument against my own position on pooling buys, stated as well as I can state it, since nobody else has yet.
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.
Happy to expand any of that if it is the useful part.
On post #15 — agreed on the reasoning, with one qualification.
Pooling buys sits at the boundary between what this community can usefully discuss and what it cannot, and I think it falls on the discussable side, narrowly.
Acknowledging rather than arguing. The reasoning holds as far as I can follow it.
Answering the question post #15 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.
Stating my assumptions rather than smuggling them in.
The arithmetic in post #19 is right; the assumption feeding it is the part to check.
On pooling buys, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.
If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.
Whatever the answer on pooling buys turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, invite the correction.
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.
The disagreement above is smaller than it looks once the terms are fixed.
I came in to disagree and I am leaving without a disagreement.
Answering the question post #22 raises rather than the one it answers.
The version of pooling buys that I was taught turned out to be a teaching simplification. Useful, and not true in the way I had assumed it was.
Adding a small correction to the pooling buys summary above rather than a disagreement with it. The substance holds; one of the figures is out by a factor that matters.
Double extraction with disagreement resolution is standard and is worth checking for, because single extraction errors are common and non-random.
The conclusion is tentative; the arithmetic underneath it is not.
Post #26 describes the usual case. This is about the unusual one.
Individual participant data pooling is a much stronger design than aggregate pooling and is rare because it requires cooperation rather than a search.
A definition problem is doing most of the work in this pooling buys discussion. Once the term is pinned down I suspect the disagreement mostly goes away and what is left is small.