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The PLOS ONE journal has an impact factor over 3. The specialist journals in my field top out with impact factors of about 3. As impact factor is in essence a measure of citations per article, it seems surprising that a journal like PLOS ONE that prides itself on not making subjective judgments on things like "importance" can maintain a higher impact factor than journals that prioritize "importance".

I have only cited handful of articles published in PLOS ONE and looking at what has been published in PLOS ONE in my field, the majority of things look "unimportant." It seems like in my specialty that PLOS ONE publishes a higher percentage of "unimportant" work than the specialist journals. This of course could be due to sample size and my own bias.

I am curious about what drives the impact factor of PLOS ONE. Are there specialties for which the PLOS ONE impact factor is low compared to specialist journals? Are editors and reviewers of specialist journals particularly bad at identifying "importance"? Is there something else?

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    I do not know about PLOS ONE specifically, but I guess part of the answer will be that impact factor is quite field-dependent. For that matter, other interdisciplinary journals manage to achieve much higher impact factors. – xebtl Sep 9 '15 at 18:15
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    While I am comparing PLOS ONE to Nature, I should note that the size of the journal is also critical. The journals with very high impact factors achieve them largely by publishing only those papers which are likely to get a large number of citations. There is an interesting editorial in PRL from a few years ago about this effect. – xebtl Sep 9 '15 at 18:26
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    Slightly more meaningfully (being based on a credible and public scoring system), the Eigenfactor of PLOS ONE is now 1.533 compared to Nature's 1.499, so overall it can be said to be more impactful, but the Article Impact is massively lower. This seems to indicate it publishes an enormous number of papers of which most only receive a few citations, whereas Nature publishes fewer papers which almost all are highly cited. – András Salamon Mar 5 '16 at 11:25
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There are, I think, two distinct factors at work that may help explain some of your puzzlement:

  • Your field's impact factor is not academia's impact factor. For example, society journals in my field have an impact factor of ~ 5, and some of the big names for very splashy studies have impact factors ranging from 20 to 56. Depending on the balance of fields submitting to PLOS ONE, their impact factor may be coming from more cited fields.
  • Long-tailed citation papers. Impact factors, like many averages, are susceptible to long-tail effects. PLOS ONE is an open-access journal, and a highly visible one. It's possible that the occasional highly accessible generalist paper makes it there, and yields a large number of citations as a result, pulling up the overall impact factor.

Both of these are helped, in my opinion, by the lack of review for "importance" - beyond your suggestion that this does result in less important papers ending up in PLOS ONE, it's also a benefit to papers that don't quite "fit" in highly specialized journals, but may still be impactful.

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    I agree with both these points, and I think they lead towards an unstated #3 - a nonselective megajournal like PLOS One may well tend towards an impact factor broadly representative of the scientific literature. Is the overall citation rate of all published papers on the order of 3 citations over two years? Someone must have studied this... – Andrew Sep 9 '15 at 20:50
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    Quick check on WoS: papers published in 2012 across all subjects were cited 3.8 times in 2014 for authors called 'White' (7k papers), 6.03 for authors called 'Black' (1.5k), 3.48 for authors called 'Green' (5k), 3.03 for authors called 'Clark' (6k); weighted average 3.83. So it's plausible. Hmmm. More work needed :-) – Andrew Sep 9 '15 at 21:00
  • The average number of citations received within two years is roughly equal to the average number of citation given to articles from the last two years by a random paper. This is very field-dependent, but 3 looks like a good ballpark estimate. – Federico Poloni Sep 9 '15 at 21:02
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    @StrongBad I'd expect it to be a bit under (because the top material in all fields certainly does preferentially go to other journals) but not dramatically so. Regarding your original query, it might be very interesting to "subdivide" PLOS One (eg 'all paleontology papers') and see how that subset compares to other topical journals... but a bit more work. – Andrew Sep 10 '15 at 9:22
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    I've just come across this study which seems somewhat relevant - leo.cineca.it/index.php/jlis/article/view/11257/10621 - about half the JCR categories have an OA title in the top quartile, and the highest-IF journal is OA in eight of them. However, none of these are PLOS One style megajournals. – Andrew Sep 16 '15 at 7:32
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I think that PLOS ONE is gambling on two key hypotheses:

  1. People are very bad at judging future importance --- thus, no "significance" filtering.
  2. Search engines and social networks are now much better at delivering articles than subscriptions --- thus, open access.

This certainly conforms with my experience: at present I have two PLOS ONE articles, each published about 5 years ago, one with 80 citations and the other with 9 citations as of this writing. Both are quite specialized and likely would have had a hard time getting published in "selective" journals, yet have found some sort of audience. I'm thus not surprised that they seem to be able to maintain a reasonable impact factor.

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    I don't think PLOS is interested in "maintaining" the journal impact factor of PLOS ONE. Many people involved with PLOS view journal impact factor metrics as actively harmful to science and scientific publishing. – Michael Hoffman Sep 10 '15 at 11:21
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    @MichaelHoffman are you kidding? It's their product: no editorial rejection and an IF that approximates the one of good journals in many fields. How else would they generate so much revenue and pay their CEO half a million a year? – Cape Code Mar 14 '16 at 8:27
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    No, I am not kidding. – Michael Hoffman Mar 14 '16 at 12:49
  • Many people involved with PLOS view journal impact factor metrics as actively harmful to science and scientific publishing. – I've seen this opinion also in no relation ton Open Access and PLOS. But, as far as I can tell, this opinion has not reached your typical tenure and search committees. Yet not? – Oleg Lobachev Sep 23 '18 at 14:41
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Note this answer is anecdotal, but since I have heard this stated by 3 high volume publishing professors now, I believe that it may be a factor. These 3 professors claimed to rank journals as follows (approximately)

  1. nature and science
  2. PNAS and the top specialized (but still fairly broad) Journal in their field
  3. All other journals including PLOS one

One philosophy for academic success is that once you have many publications in reasonably good journals, the marginal benefit of one more isn't that great. However, the marginal benefit of one more Science or Nature paper is quite big. Therefore, since PLOS one is often less of a hassle to submit to, if a paper is rejected from Science or Nature or PNAS the next stop for these high impact professors is often PLOS one. It just isn't worth it for these busy professors to trudge through multiple submissions down the journal food chain because they want to focus on their next Science/Nature submission or Grant proposal which could lead to such a paper. This means PLOS one gets a lot of papers that are written by pretty famous professors that just weren't jazzy enough for Nature and Science. Of course, PLOS one also gets a bunch of unimportant papers (by famous and non-famous authors) but I suspect some of the heavy tail papers that @fomite suggested are from academics with this philosophy.

I again stress that this is anecdotal and that I have no data to confirm this hypothesis.

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    I think this is quite possible. – StrongBad Mar 13 '16 at 16:44
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While PlosOne ostensibly publishes papers from all fields of science, it is heavily weighted towards biology and medicine. Journals in these fields have higher impact factors because (a) they have more references per paper (I'd hypothesise that this might also be related to the use of numeric citations rather than apa/harvard style), and (b) they have shorter reference half-lives (i.e., papers accrue a greater proportion of their total references in the two to three years post-publication period that is used to calculate impact factor).

These are purely idiosyncratic factors that influence the average impact factor of journals in a particular field.

  • If you come from a field in biology or medicine, you might see an impact factor of 3 as perhaps average or a bit above average.
  • In psychology where I come from, some of the best journals in a given subdiscipline have impact factors in the 3 to 6 range.
  • In other fields like mathematics or the humanities, an impact factor of 3.0 would be perceived to be even greater.

The main point is that impact factors are more highly correlated with subjective evaluations of quality and importance when such comparisons are performed for journals within a discipline.

In addition, even relative to fields like medicine and biology, the impact factor for PlosOne is respectable. Articles are clearly being cited quite a bit in these areas. You can see more information by going to scimago or Web of Science Citation Reports.

If you want to compare journals in a more discipline-neutral way, you might want to look at the SJR. It uses an iterative weighting procedure which I believe weights references coming from more prestigious journals more highly and allows each article to only give away a finite amount of prestige. So for example, an article with many citations can only give fractional prestige. This allows disciplines with more references per paper to count a little less.

For example, on that metric, PlosOne has an SJR of 1.3. In contrast, a psychology journal I know which has a similar impact factor to PlosOne had an SJR or 1.8, presumably adjusting for the different citation practices and relative prestige of source publications. You might want to look up the SJR of journals in your field to compare.

As an aside, metrics of impact at plosone have declined substantially in recent years (compare 2010 to 2016); albeit, it is still a first quartile ranked journal. Two possible explanations: (1) as a multidisciplinary journal, the mix of articles the proportion of articles coming from disciplines with high numbers of citations has declined, or (2) the average quality/impact of the research has declined.

enter image description here https://www.scimagojr.com/journalsearch.php?q=10600153309&tip=sid&clean=0

3

The answer to this question is given by the Central Limit Theorem. Basically PLoS ONE is so large that is samples the population of all papers out there, which together (if published in a single, catch-all journal) have an IF=3. In statistics this is called "regression to the mean."

For more info, please see my paper "Impact Factors and the Central Limit Theorem: Why citation averages are scale dependent" in the Journal of Informetrics.

1

The key selling point of a top-tier journal is not that the content is more important, rather, their standards for publishing in general are much higher. Of course one criteria is impact, but arguably the most important criteria is the level at which the peer review is done. I've seen papers requiring 3 or 4 new experiments to please reviewers in Cell/Nature.

What difference does going-the-extra-mile in due diligence have on a paper's citation rate? I doubt little if any. People cite publications relevant to their work, regardless of how many replicates that cited paper used or how many supplementary figures there are. Of course, high-impact journals have other criteria that does push up the citation rate, such as impact, but my point is that it's a false assumption to assume the only thing going for top-tier journals is their impact requirements.

  • A reviewer asking for replication is not uncommon in any journal. Plos one is pretty rigorous about the quality of the science (arguably just as much as nature, although likely more variable given the number of papers handled). I don't buy this explanation. – WetlabStudent Mar 14 '16 at 9:37
  • @WetLabStudent pretty rigorous about the quality of the science indeed. – Cape Code Mar 14 '16 at 13:35
  • @CapeCode I knew someone was going to bring this up. Considering plos one publishes 85 papers a day, about 50 times more frequent than even the most prolific journals (e.g. Nature), if Nature and Plos one were equal quality you'd expect Plos one to have about 50 times more ridiculously bad publications that slipped through the crack than nature. I know of many papers that have been rejected by plos one and then successfully published in reasonably good (Q1) non-open access journals. – WetlabStudent Mar 14 '16 at 15:37
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    @WetLabStudent thanks for bringing up the staggering volume figures, one more factor of course is that PLOS makes money every time it accepts a paper. A strong incentive to accept more papers. – Cape Code Mar 14 '16 at 16:09
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    That adds up to 46 million $/year in revenue, no wonder they advocate the obsolescence of editorial rejection. – Cape Code Mar 14 '16 at 16:13
0
  1. The large number of papers published by PLoS ONE may increase the likelihood of some being very highly cited. This may drive up the Impact Factor.
  2. I agree it may also reflect the average (geometric or arithmetic) across all journals. Because PLoS ONE publishes a lot of biology, especialy biomed papers, these tend to be more cited because it is a larger field (e.g. compared to geology or statistics).
-3

One thing that seems to have been left out of this thread is the volume of articles published by PLOS ONE. Approximate 85 per day according to their wikipedia page. It seems that that would argue against a long tail effect.

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    Why do you think that would argue against a long tail effect? it seems to me that the high number of samples would actually make it easier for the long tail to occur. – jakebeal Mar 4 '16 at 16:30

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