Monday, October 20, 2014

Journal "quality"

Anurag Acharya and co-authors from Google Scholar have a pre-print at entitled Rise of the Rest: The Growing Impact of Non-Elite Journals in which they use article-level metrics to track the decreasing importance of the top-ranked journals in their respective fields from 1995 to 2013. I've long argued that the value that even the globally top-ranked journals add is barely measurable and may even be negative; this research shows that the message is gradually getting out. Authors of papers subsequently found to be "good" (in the sense of attracting citations) are slowly but steadily choosing to publish away from the top-ranked journals in their field. You should read the paper, but below the fold I have some details.

Acharya et al:
attempt to answer two questions. First, what fraction of the top-cited articles are published in non-elite journals and how has this changed over time. Second, what fraction of the total citations are to non-elite journals and how has this changed over time.
For the first question they observe that:
The number of top-1000 papers published in non-elite journals for the representative subject category went from 149 in 1995 to 245 in 2013, a growth of 64%. Looking at broad research areas, 4 out of 9 areas saw at least one-third of the top-cited articles published in non-elite journals in 2013. For 6 out of 9 areas, the fraction of top-cited papers published in non-elite journals for the representative subject category grew by 45% or more.
and for the second that:
Considering citations to all articles, the percentage of citations to articles in non-elite journals went from 27% in 1995 to 47% in 2013. Six out of nine broad areas had at least 50% of citations going to articles published in non-elite journals in 2013.
They summarize their method as:
We studied citations to articles published in 1995-2013. We computed the 10 most-cited journals and the 1000 most-cited articles each year for all 261 subject categories in Scholar Metrics. We marked the 10 most-cited journals in a category as the elite journals for the category and the rest as non-elite.
In a post to liblicense, Ann Okerson asks:
  • Any thoughts about the validity of the findings? Google has access to high-quality data, so it is unlikely that they are significantly mis-characterizing journals or papers.They examine the questions separately in each of their 261 subject categories, and re-evaluate the top-ranked papers and journals each year.
  • Do they take into account the overall growth of article publishing in the time frame examined? Their method excludes all but the most-cited 1000 papers in each year, so they consider a decreasing fraction of the total output each year:
    • The first question asks what fraction of the top-ranked papers appear in top-ranked journals, so the total volume of papers is irrelevant.
    • The second question asks what fraction of all citations (from all journals, not just the top 1000) are to top-ranked journals. Increasing the number of articles published doesn't affect the proportion of them in a given year that cite top-ranked journals.
  • What's really going on here? Across all fields, the top-ranked 10 journals in their respective fields contain a gradually but significantly decreasing fraction of the papers subsequently cited. Across all fields, a gradually but significantly decreasing fraction of citations are to the top-ranked 10 journals in their respective fields.  This means that authors of cite-worthy papers are decreasingly likely to publish in, read from, and cite papers in their field's top-ranked journals. In other words, whatever value that top-ranked journals add to the papers they publish is decreasingly significant to authors.
Much of the subsequent discussion on liblicense misinterprets the paper, mostly by assuming that when the paper refers to "elite journals" it means Nature, NEJM, Science and so on. As revealed in the quote above, the paper uses "elite" to refer to the top-ranked 10 journals in each of the individual 261 fields. It seems unlikely that a broad journal such as Nature would publish enough articles in any of the 261 fields to be among the top-ranked 10 in that field. Looking at Scholar Metrics, I compiled the following list, showing all the categories (Scholar Metrics calls them subcategories) which currently have one or more global top-10 journals among their "elite journals" in the paper's sense:
  • Life Sciences & Earth Sciences (general): Nature, Science, PNAS
  • Health & Medical Sciences (general): NEJM, Lancet, PNAS
  • Cell Biology: Cell
  • Molecular Biology: Cell
  • Oncology: Journal of Clinical Oncology
  • Chemical & Material Sciences (general): Chemical Reviews, Journal of the American Chemical Society
  • Physics & Mathematics (general): Physical Review Letters
Only 7 of the 261 categories currently have one or more global top-10 journals among their "elite". Only 3 categories are specific, the other 4 are general. The impact of the global top-10 journals on the paper's results is minimal.

Lets look at this another way. No matter how well their work is regarded by others in their field, researchers in the vast majority of fields have no prospect of ever publishing in a global top-10 journal because those journals effectively don't publish papers in those fields. And if they ever did, the paper is likely to be junk, as illustrated by my favorite example, because the global top-10 journal's stable of reviewers don't work in that field. The global top-10 journals are important to librarians, because they look at scholarly communication from the top down, to publishers, because they are important to librarians so they anchor the "big deals", and to researchers in a small number of important fields. To every one else, they may be interesting but they are not important.

Acharya et al conclude:
First, the fraction of top-cited articles published in non-elite journals increased steadily over 1995-2013. While the elite journals still publish a substantial fraction of high-impact articles, many more authors of well-regarded papers in diverse research fields are choosing other venues.

Second, now that finding and reading relevant articles in non-elite journals is about as easy as finding and reading articles in elite journals, researchers are increasingly building on and citing work published everywhere. 
Both seem right to me, which reinforces the message that, even on a per-field basis, highly rated journals are not adding as much value as they did in the past (which was much less than commonly thought). Authors of other papers are the ultimate judge of the value of a paper (they are increasingly awarding citations to papers published elsewhere), and of the value of a journal (they are increasingly publishing work that other authors value elsewhere).


David. said...

Steven Levy at has a long profile of Anurag Acharya.

David. said...

The idea that top-ranked journals both add and subtract value is often received skeptically. Here's just one example from the literature showing that this result is well-established.

The editors of Infection and Immunity in 2011 reflected on a spate of recent retractions and wrote a paper Retracted Science and the Retraction Index. They conclude:

"Using a novel measure that we call the “retraction index,” we found that the frequency of retraction varies among journals and shows a strong correlation with the journal impact factor."

For a more radical take on this effect, see my blog post Journals Considered Harmful.

David. said...

Of course, everyone makes mistakes, but this example of the lack of publisher added value is too good to overlook.

David. said...

Oops, sorry, I finally noticed that the link in the previous comment is bogus. Here is the correct link.