Preprint servers and what screening they do — the long version

On the subject in the title: Preprint servers and what screening they do — the long version Working notes rather than a conclusion.

A preprint question rather than a question about the finding in it.

The manuscript is on a preprint server, dated, with a version number I have written down. It has not been through review and the authors say so in the header. What I cannot work out is how much weight that leaves it carrying.

I would like the reasoning rather than a rule. "Wait for publication" is not usable when the publication may be two years away and the question is now.

Server repositories: medRxiv for medicine, bioRxiv for biology. Preprints on these servers are time-stamped and have DOIs even if they are later published elsewhere. Citing the preprint with its DOI is appropriate while noting it is unpublished.

I would rather say I do not know than round it up to an answer.

Confirming post #2 from a second method, which matters more than confirming it from a second person.

Check whether it was later published: searching for the preprint's first author and keywords in PubMed might find a published version. The published version is the stronger citation if it exists.

Reading a preprint properly means doing some of the reviewer's job: methods first, then whether the analysis matches the plan, then the conclusion.

Nothing above should be read as advice about what anyone else should do.

If you cite a preprint in a maintained document here, the convention is to label it in the sentence and to note the check date. The document review will catch the update.

It is the kind of thing that is obvious once and never again.

A preprint that has been up for two years without appearing in a journal is telling you something, and it is not necessarily that the work is bad.

Where I would look next, rather than where I would stop.

Post #6 is the version of this I will quote in future. One addition.

Say it is a preprint in the first line rather than the last. Everything downstream depends on that status and readers arriving from search will not scroll for it.

Where I part company with post #4, and it is a narrow parting.

Unrefereed work is not worthless. A great deal of it survives review substantially unchanged. It is also the case that the version appearing in a journal frequently has different numbers, and the changes are not random — they tend to be in the direction of a smaller effect and a more careful claim.

Narrowing post #6, because the general version has more than one answer.

Where a preprint's numbers are the basis of a claim being repeated here, someone should check whether the published version exists yet. That check is nearly always overdue.

Where a preprint contradicts a published trial, the prior should favour the trial. Where it extends one, the preprint can be genuinely useful.

Sample size and pre-registration are checkable in a preprint exactly as in a paper, and they carry the same weight.

What changes between preprint and publication: authors respond to reviewer comments, re-analyse data, correct errors found in peer review, and sometimes report different results from updated analyses. The published version is not the same as the preprint.

Not the whole picture, but the part of it I can speak to.