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When researchers submitted a paper about a type of microparticle to PNAS, they wanted to give credit where it was due, and cite an unpublished manuscript that helped guide their work. But the journal’s policy forbid citing unpublished work, and the reference was removed before publication. Now, concerns from the authors of that unpublished work have prompted the journal to have a change of heart.
The 2017 PNAS paper focused on microswimmers, which are engineered “to self-propel in a fluid.” Microswimmers have potential applications in targeted drug delivery and surgery, but guiding their motion remains a challenge. In the paper, corresponding author Jean-Baptiste Delfau and his colleagues at the University of Tokyo described a strategy to do so using an electric field. But, as a recently issued correction notice acknowledges, these findings were influenced by another group’s work. (The authors of the initially uncited manuscript argue their paper was even more influential than the authors claim.)
A spokesperson for PNAS told Retraction Watch that, shortly after publication, two chemists—Haw Yang, a professor of chemistry at Princeton University in New Jersey, and Markus Selmke, a former postdoc in Yang’s lab—contacted the journal concerning “overlap” with their unpublished manuscript. According to the spokesperson, the PNAS authors had cited Yang and Selmke’s work when they submitted their draft, but copy editors removed it in proofs because:
PNAS does not allow citation of unpublished manuscripts. Readers should have access to references to verify the information being cited.
In this instance, however, the journal changed its mind. The spokesperson told us:
The Editorial Board felt it was important for readers to have the information in this particular instance.
In the lengthy correction for “Optimal run-and-tumble–based transportation of a Janus particle with active steering,” the authors explained that while writing their manuscript “we had access to an unpublished preprint from the Princeton group of H. Yang and coauthors,” which dealt with the motion of these microswimmers. (The preprint had not been published on arXiv or another server.)
According to Selmke, the Yang lab had shared three unpublished manuscripts with Tomoyuki Mano, first author on the PNAS paper, “in good faith, explicitly as unpublished internal drafts” when he was a graduate student in Yang’s lab. But, Selmke explained, after Mano moved to the University of Tokyo (where last author Masaki Sano works), the unpublished work was:
… shared and used without our knowledge or consent among the (external) authors of the PNAS article. …
Selmke told us that the authors of the PNAS paper—cited five times since it was published in March 2017, according to Clarivate Analytics’ Web of Science—used some of the results and ideas from the manuscripts knowing “part of their published results were based on our entirely uncredited work, presented as their own.”
But Delfau, corresponding author on the PNAS paper and a postdoctoral researcher at the University of the Balearic Islands in Mallorca, Spain, said the unpublished manuscript had a “quite faint” influence on their work:
It only gave us the idea of using in our own calculations a function that was published in 1953. Considering that we did not use any of [Yang and Selmke’s] results in our own study, we considered that [removing the reference] was not such a big deal at the time.
Selmke told us that he and his co-authors had informed PNAS of their concerns last May.
Despite this incident, the spokesperson told us:
We are not modifying our policy on citing unpublished manuscripts.
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PNAS allows citation of personal communications in this context. They only are not allowed under this rule: “Data not shown and personal communications cannot be used to support claims in the work.” (ie nothing that hasn’t gone through peer review should need to be assumed true to buy your conclusions). Probably the same applies to preprints.
But it’s still 1000% citable if it’s essential background information or you’re claiming that this was your 100% original idea.
Why would you want to cite an unpublished manuscript? At the very least it should be accepted for publication.
It’s quite common in mathematics, at least, for authors of a paper to acknowledge people whose ideas have influenced the results proved in that paper—even ideas that are unpublished (not even on the arXiv), not necessarily accepted for publication, perhaps not written down! Of course such ideas should not and would not be used to “support claims” of the authors, unless the authors either provided proofs (their own, or the originator’s suitably acknowledged) or (in exceptional cases, of which I cannot actually think of an example) stated that the ideas were X’s “conjecture” or “hypothesis” or “Jugendtraum“.
I’ve been on both sides of such sharing rituals, and I think they’re valuable. But the practice of mathematics differs in many ways from those of the various sciences.
I post the majority of my work on arXiv before publication. One time another group published a paper where they copied the *style* of a figure from one of my preprints. It was a 3D rendering of a particular concept and there are many possible ways to color that image, but if you saw our version and their version it’s obvious that they are intentionally similar. Their article was published a month before us, and did not cite our preprint, I was told because the senior author does not believe in citing unpublished work. Uh, because it’s important that the style of a figure be peer-reviewed?
So yeah, I agree that unpublished work should not be used to support key claims. But “Why would you want to cite an unpublished manuscript?” There’s many reasons to cite work that have nothing to do with whether that work is unpublished or peer-reviewed.