The growing divide between higher and low impact scientific journals

Ten years ago the Public Library of Science started one big lower impact and a series of smaller higher impact journals. Over the years these publication outlets diverged. The growing divide between standard and top journals might mirror wider trends in scholarly publishing.

There are roughly two kinds of journals in the Public Library of Science (PLoS): low impact (IF = 3.06) and higher impact (3.9 < IF < 13.59) journals. There is only one low impact journal, PLoS ONE, which is bigger in terms of output than all the other journals in PLoS combined. Its editorial policy is fundamentally different to the higher impact journals in that it does not require novelty or ‘strong results’. All it requires is methodological soundness.

Comparing PLoS ONE to the other PLoS journals then offers the opportunity to plot the growing divide between ‘high impact’ and ‘standard’ research papers. I will follow the hypothesis that more and more information is required for a publication (Vale, 2015). More information could be mirrored in three values: the number of references, authors, or pages.

And indeed, the higher impact PLoS journal articles have longer and longer reference sections, a rise of 24% from 46 to 57 over the last ten years (Pearson r = .11, Spearman rho = .11), see also my previous blog post for a similar pattern in another high impact journal outside of PLoS.

plos-not-one_more-and-more-references-over-time

The lower impact PLoS ONE journal articles, on the other hand, practically did not change in the same period (Pearson r = .01, Spearman rho = -.00).

plos-one_same-references-over-time

The diverging pattern between higher and low impact journals can also be observed with the number of authors per article. While in 2006 the average article in a higher impact PLoS journal was authored by 4.7 people, the average article in 2016 was written by 7.8 authors, a steep rise of 68% (Pearson r = .12, Spearman rho = .19).

plos-not-one_more-and-more-authors-over-time

And again, the low impact PLoS ONE articles do not exhibit the same change, remaining more or less unchanged (Pearson r = .01, Spearman rho = .02).

plos-one_same-author-count-over-time

Finally, the number of pages per article tells the same story of runaway information density in higher impact journals and little to no change in PLoS ONE. Limiting myself to articles published until late november 2014(when lay-out changes complicate the comparison), the average higher impact journal article grew substantially in higher impact journals (Pearson r = .16, Spearman rho = .13) but not in PLoS ONE (Pearson r = .03, Spearman rho = .02).

plos-not-one-is-getting-longer

plos-one-is-not-getting-longer

So, overall, it is true that more and more information is required for a publication in a high impact journal. No similar rise in information density is seen in PLoS ONE. The publication landscape has changed. More effort is now needed for a high impact publication compared to ten years ago.

Wanna explore the data set yourself? I made a web-app which you can use in RStudio or in your web browser. Have fun with it and tell me what you find.

— — —
Vale, R.D. (2015). Accelerating scientific publication in biology Proceedings of the National Academy of Sciences, 112, 13439-13446 DOI: 10.1101/022368

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2 comments

  1. Thanx for the data analysis! Once more, very interesting to get something empirically proven what I observed subjectively during the last years. But I am not sure about the interpretation. E.g., the number ov authors might not reflect the need for more content contributors but the pressure to publish. Many colleagues in my network build publication guildes, everyone puts everyone on the author list. Such a tactic is more charming with journals of higher impact.

    Keep on, Richard! 🙂

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