Comparing the Impact of Journals

Yesterday the JGR Space Physics editors had their quarterly telecon and we talked a bit about the new Journal Impact Factor (JIF) that was just released. We want the journal to be very high quality but we do not want to be metrics manipulators. We agreed to monitor it for the next few years.

The topic of metric reliability is on the minds of many journal editors. Martyn Clark, the Editor in Chief of AGU’s journal Water Resources Research, just published an Editorial entitled, “The citation impact of hydrology journals,” coauthored by Brooks Hanson, AGU’s Director of Publications. It analyzes several metrics for 6 hydrology-related peer-reviewed journals for the past ~20 years. It’s a very nice examination of journal metrics for a geophysics field. I encourage you to read it.

Let me summarize the key findings. They show that all of the journals have the same temporal trend in their metrics, with the JIF steadily rising, in general, for all hydrology journals over the last 15 years. They also see significant variability in the JIF of smaller journals (i.e., those that publish < 200 articles per year) as a few highly-cited papers skew the JIF upwards for a year or two, quantified by resampling the articles to create a uncertainty spread on the metric. All of the journals had Lost Papers with zero citations and Super Papers with >100 citations. They find hydrology papers taking a relatively long time to “mature” and reach full influence on the field, a similar trend as in space physics, as evidenced by most citations occurring after the 2-year window of the JIF (compare their Figures 6 and 7 with a similar plot for JGR Space Physics here). The main finding of the article is that journal metrics, in particular the JIF, are temporally variable, have relatively large spreads of uncertainty, and are not representative of the influence of a specific paper on its research field.

The JIF is reported to 4 significant digits, but this Editorial clearly demonstrates that this level of precision is overkill. Here is a plot of the spread of JIF values for 3 of the journals:


JHM is the smaller of these 3 and the uncertainty in its JIF is > 0.5. The other two journals publish 500-800 articles per year, so their uncertainties are lower, but they are still several tenths of a point.

They bring up a fantastic point that I want to repeat here: citations to a paper do not necessarily measure the quality of the paper, but rather represent the utility of the paper. Citations show that others are building on the findings of the paper but the number of citations does not capture the robustness of the analysis within the paper. I don’t think that we have a good measure for that yet.

If you look at the Acknowledgments, Jennifer Satten at Wiley provided the bibliometrics data for this article. She has given me much of the same information for the field of space physics. I could work up a similar article for our discipline. It’s on my to-do list. Maybe I will, or perhaps I’ll just show some plots in this blog as I make them.


JGR’s 2016 Impact Factor

Clarviate Analytics, the new company name for the part of Thomson Reuters that makes the Journal Citation Reports, just released the 2016 Journal Impact Factors. As expected, they separated the sections of JGR into different journals, giving each one its own JIF. And the value for JGR Space Physics is … wait for it … 2.7.


            As I wrote back in January his is what I was expecting. Actually a little higher, which is nice. While this is a big drop from last year’s “all sections of JGR” value of 3.3. The JGR Space Physics JIF score is the lowest of the JGR family, just below JGR Oceans (at 2.9) and a full point below JGR Planets (at 3.7).

I am not that concerned about it. I gave several reasons for this back in January, especially the fact that we have a near linear growth in the average citations per paper for the first decade after publication. That is, the average citations per 10-year-old paper is right at 30. On average, we cite each paper ~3 times per year, every year, for a long time after publication. Here’s the graph I showed in January supporting this:


This is not the only good news about the longevity of JGR Space Physics papers: the cited half life is over 10 years (the maximum that Clarviate Analytics posts, “>10.0”). So, on average, a 10-year-old paper has yet to reach half of its total citations over its lifetime. This means that the average JGR Space Physics paper will eventually reach a total citation count of over 60.

Another bright spot: our Immediacy Index is 0.71, which is second among the JGR family. This is the number of citations in the year 2016 to papers published in the year 2016. For reference, a quick scan over the last 5 years of values reveals that only one AGU journal, Reviews of Geophysics, has an Immediacy Index over one (it jumps between 1 and 3, with its 2016 value being 2.3). I have not analyzed whether this is from a few papers getting many citations or a broad spectrum of papers getting a few, but either way, I’d say that we’re doing pretty well at reading the new literature. Way to go!

Our field of space physics has a particular way of citing publications. Some papers get immediate attention resulting in citations within the first year but most papers take a while to be absorbed by the community and achieve their full impact on the field. In the long run, JGR Space Physics papers are highly cited.

AGU’s Commentary Collections

A Commentary is an AGU paper type that offers a perspective on a recent result, controversy, or special event in particular field. JGR Space Physics published 15 Commentaries in 2016, most of them as part of the special section on Unsolved Problems in Magnetospheric Physics. These short articles are meant to spur discussion, action, and hopefully eventual resolution regarding the chosen topic. In JGR Space Physics, they are too new to understand and quantify their influence. Other journals have published Commentaries for many years, and the anecdotal evidence is good enough that AGU is encouraging all journals to publish more of these.

To better highlight and promote the existence of these papers, AGU has assembled several new special collections that gather these Commentaries for easy discovery. The link is on all journal websites, under the Special Collections pull-down menu:


On this page are links to the Commentaries in each AGU discipline, including Space Weather and Space Physics. There are Commentaries here from a few different journals. Because papers cannot be in two special sections in the Wiley paper management system, instead of listing all of the UPMP Commentaries, there is simply a link to that special section’s webpage.

Happy reading!


Want Some Salt With That Metric?

I’ve become a fan of the Scholarly Kitchen. It’s a multi-author blog produced by the Society for Scholarly Publishing. They have daily posts about academic publishing across a wide range of topics, including some useful categories for JGR Space Physics readers, like peer review, discovery and access, and a category simply called academia.


While at the AGU EiC meeting this week, a link to a just-posted Scholarly Kitchen article was circulated on the trustworthiness of journal metrics. The author rates the various journal metrics according to their completeness, transparency, and veracity. She uses a clever scale…the “grains of salt” with which you should take each of the metrics. It goes well with my recent posts on metrics.

And the winner is…CrossRef, which only requires a pinch of salt. ISI and Scopus should be taken with a cup of salt, Download Statistics with a bathtub of salt, and Google Scholar and Research Gate with a classroom full of salt. Yeah, she really doesn’t like Google Scholar for scholarly metrics.

The author is Angela Cochran, who is the Journals Director for the American Society of Civil Engineers and a Past-President of the Council of Science Editors. She knows what she’s talking about on this subject.

I like one of the comments on the article about defining a new SI unit for skepticism, the pinch. A cup of salt is then a kilopinch, a bathtub a megapinch, and a classroom is a gigapinch. Clever.

CrossRef is what is used by Wiley for the “Cited By” link on each paper for all AGU journals, including JGR Space Physics. Here’s a recent example article with a healthy number in the “cited by” tab. When a publisher prepares a paper for production, they check the references for compliance with the database of known scholarly literature. Once published and online, that paper’s link is sent to CrossRef, which resolves the reference tags against its vast database, ensuring that the citation from the new paper is counted in the “cited by” list for each cited reference in it. The system is fast and the linkages are automatically made. CrossRef is a non-profit organization to which nearly all publishers contribute and subscribe, meaning that the database is as robust as possible and yet focused only on scholarly content.

CrossRef does not take the next step of generating an Impact Factor or CiteScore, which are proprietary creations of Thomson Reuters and Elsevier, respectively. What you get with CrossRef is a near-instantaneous update of the “cited by” number and paper listing at the Wiley site for your papers in AGU journals, and you can trust that it is the most accurate count of citations to your paper from other scholarly publications. That’s okay with me. We need to be dishing out kilopinches (or more) of salt with those other metrics, anyway.

Impact Factor Just For JGR-Space Physics

This coming year, I am told that Thomson Reuters will release section-specific Journal Impact Factors for JGR. I want to give the community a heads-up on where we stand.

If your institution has a subscription to Thomson Reuter’s Web of Science, then it is not a difficult to do a search for “Journal of Geophysical Research Space Physics” in the “Publication Name” field for specific years (one at a time) and get the citation numbers for a Journal Impact Factor specific for JGR-Space Physics.

I just did this and here are the results:


Unofficial JIF for JGR-Space Physics:

Number of items published in 2014:              760

Number of items published in 2013:              711

Cites in 2015 to items published in 2014:      1808

Cites in 2015 to items published in 2013:      2077

My estimate of the 2015 JGR-Space Impact Factor =      3885 / 1471 = 2.64


Hmm. This is well below the JGR-all sections JIF of 3.3 reported by Thomson Reuters. When I do this same search but with “Journal of Geophysical Research *” for the publication name, then I get a value of 3.20. This is close but a bit lower than the Thomson Reuters value. This is expected because I did not remove Editorials, Prefaces, and other items from the list of “papers”, which presumably have few if any citations and which presumably Thomson Reuters removes from the JIF calculation. So, perhaps the JGR-Space Physics value that I just calculated should be up by a tenth or two, but most likely it is still below 3.0.

I gathered the numbers for the 5-year Impact Factor, and for 2015, JGR-Space Physics has 2.76. Better than the 2-year JIF above, as expected because the journal has such a long cited half-life. With the correction to the denominator, this value is approaching 3.0, but again, probably not all the way up to it.

I was a nerd about it and pulled values back to 2002, when JGR went digital. This gives me 2-year JIF scores back to 2004 and 5-year JIF scores back to 2007. With my simple method, there has only been one 2-year JIF for JGR-Space Physics above 3.0, in 2012. The lowest is in 2004, which I calculate to be 1.89, but I am not sure that I trust the citation numbers for 2002; they are noticeably lower than other years and it is the year of the “switch.” So, removing this, then the next lowest year is 2007, with 2.25. Most years are between 2.5 and 2.7.

What does this mean? It means that this is the “level” for the JIF of JGR-Space Physics. Adding in the “Immediacy Index” values (cites in the same year as publication), which are usually between 0.6 and 0.8, and the total number of citations in the first two years of a paper’s life is, on average, between 6 and 6.5.

Note that the number of papers without a citation at all is very low. After 2 years, it is already down to just a few percent. Nearly all papers are cited at least once. In fact, total citations for the average paper increases almost linearly for the first ~8 years or so, as seen here:


I’d say that’s pretty good.

In fact, it is a big reason why I am not afraid of the coming official release of a JIF specific to JGR-Space Physics and its expected value of below 3.0. This journal’s papers have longevity, accumulating citations well past anyone’s journal metric calculations. People have published good papers in this journal, and present-day researchers continue to cite those studies. We take a while to absorb a result and build on it. The JIF is useful as a journal metric, but it is not the whole story.

JIF and CiteScore

This week, Physics Today published an article on the Journal Impact Factor and the new CiteScore index. Both are average citation values within a certain year to papers published in a few preceding years. The main difference between the two are that the JIF uses citations to papers in the prior two years while CiteScore includes citations to papers in the previous three years. The other main difference is that Elsevier, the creator of the new CiteScore index, is making everything about the creation of the values open, while Thomson Reuters only makes the formula and numbers used available to subscribers, and the actual list of citations is kept proprietary.


            As the Physics Today article notes, the values are similar for most journals between the two indices, but some shifting is evident, especially among the top titles. For JGR (all sections combined), the values are almost identical, with the 2015 Impact Factor being 3.32 and the CiteScore being 3.39 (to two significant digits, which I don’t like to do).

Also as noted in the Physics Today article, the similarity in how they are calculated suggests that the complaints about JIF are largely applicable to CiteScore. Okay, it includes another year, but Thomson Reuters already produces a 5-year Impact Factor, so CiteScore splits the difference. Both are susceptible to the size of the “highly cited tail” of the paper distribution in a journal, especially if the number of citable items is relatively small. Also, both are susceptible to manipulation, if publishers were to unethically push authors of new manuscripts into citing papers in their journals.

I find it bewildering that there are ~5% of journals in existence with a CiteScore of zero (as reported in the Physics Today article). This means that there was a year in which there were no citations to any of the articles published in that journal for the prior three years. I have not looked up the names of these journals to look for a trend or commonality but, regardless…wow. Thanks again for reading and citing the papers in JGR Space Physics!

Details of JGR’s 2015 JCR

Thomson Reuters has completely reformatted the Journal Citation Reports (JCRs) at their website, but eventually I was able to sift through the new layout and find most of what I wanted. One of the documents, the Journal Profile Grid, is an Excel sheet in 5-point font. While this is easily correctable, it is annoying on first reading.

As I mentioned in a post last month, 2015 had flat-to-slightly-down 2-year and 5-year Impact Factors. However, in the long term, JGR‘s Impact Factor has been trending slightly upward. It was never above 3.0 in 2007 and earlier, yet has never been below 3.0 from 2008 onward. Here is a nice little graphic from the JCR showing that trajectory:


So, it’s done this (a brief, small dip) before. The little hiccup as of late might be just that, a blip in the long-term upward trend. Or it could be the start of something bad. Let’s hope for the former, not the latter.

Following what I did last year with JCR details, here are some other tidbits of information about JGR.

  • Total cites: rose by ~5% to an amazing 198,000. This is a huge number for a discipline-specific journal. Here’s a chart of JGR total cites by year:


  • Self cites: down a little at 18%. I don’t actually know what this means. A high number (above 10%, say) could be a sign of dominance in the field or it could be a sign of isolation and disconnection from the field. We’ll go with the former.
  • Immediacy index: dropped just a bit to 0.61. Remember, this is cites in 2015 to JGR papers published in 2015; most of the papers in the second half of the year have zero citations.
  • Cited half-life: still greater than 10 years. So, on average, more than half of the citations to a JGR paper occur 10+ years after its publication.
  • Citing half-life: ever-so-slightly up to 9.4 years. This is the “age” of references in JGR
  • References per paper: up by one to 56. They count papers with more than 100 references as “review articles” rather than “regular” research papers.
  • Eigenfactor score: dropped ever-so-slightly to 0.31. This value is based on the 5-year Impact Factor but removes self-cites and then weights citations based on the strength of the citing journal. This is a decent value.
  • Article Influence Score: down a bit to 1.39. This is a discipline-normalized version of the Eigenfactor. Values above unity are good.

All of these metrics are explained in more detail in an earlier post. And again, remember, this is for all of JGR, not just JGR Space Physics.


JGR’s 2015 Impact Factor

Thomson-Reuters released the 2015 Impact Factors and the value for Journal of Geophysical Research is 3.3. This is a 0.1 drop from the journal’s Impact Factor of 3.4 in 2014 and 2013 . Basically within the noise of year-to-year variation, but it went down a tenth instead of up, which is disappointing.

Here’s the Thomson-Reuter’s logo, just so we have a graphic to go with this post, with a link to their page on this topic:


            The Impact Factor is calculated as the average citations in year 2015 of papers published in 2013 and 2014. Thomson-Reuters also calculates a 5-year Impact Factor and the 2015 value for JGR is 3.7, again identical to the 2013 and 2014 values to two significant digits.

Thomson-Reuters still has all sections of JGR combined in this value. So, I don’t know what it is specifically for JGR Space Physics.

In good news for the space physics community, AGU’s Space Weather Journal rose from 2.1 to 2.4 in its 2-year Impact Factor, and from 1.9 to 2.3 in its 5-year Impact Factor. Woohoo for Space Weather!

Like last year, I’ll download the Journal Citation Report, take a closer look at the numbers behind this index, and write a follow-up post.

Passing 50000 Hits

An arbitrary but round-number milestone was reached this week: this JGR Space Physics blog passed the 50 thousand hits mark. Here’s the image from the bottom of the screen, as of a few minutes ago:


Thank you very much to all of the readers of this blog out there, whether you are regular or one-time-only visitors. Watching this number steadily rise lets me know that this effort is worth it.

Here are a few other stats about the blog readership. First, here’s a plot of the daily visitors and page views (i.e., hits) for the last month:


The numbers at the bottom are the values for today, as of a few minutes ago. As you can see, the blog normally gets between 50-100 page views a day, with a bit less on the weekends. The huge spike on May 9 is when my monthly highlights announcement came out in the SPA Newsletter. Those days typically get several hundred hits.

Here is a chart of the visitors and views per month for the last year:


The values at the bottom are for June, which is only three and a half days old. You can see that the blog hovers in the ~2000 views/month range, except for January, which I took off from blogging. That month still had ~1400 visits.

Here are the top 10 blog posts viewed so far in 2016:


            The “home page” is the most commonly visited, and on this page people can read the latest five posts. Interestingly, the next four are all from 2014. I struck on a good topic with those, and for the most part they are instructive posts on how to understand the AGU manuscript process. Only three on this top-10 list are from this year, but the “home page” views are also view of this year’s posts, so that should count, too.

Most of the readers are from the United States. Here’s the map of 2016 views by country:


It’s a little easier in table format; here are the top ten countries visiting the blog in 2016:


Countries from almost every continent are on the list. Thanks for being such a diverse audience.

One final factoid: I’ve written 162 blog posts (this is number 163). I’m two and half years into my four-year term as Editor in Chief, so I am pretty safe in saying that the majority of blog posts have already been written, unless I really pick up the pace in the final year. Please keep the blog post suggestions coming; I eventually get around to writing about most of them. If it seems that I’ve lost one of your suggestions, please feel free to send it in again.

Reviewer Statistics for 2015

We, the five Editors of JGR Space Physics just published an Editorial thanking the 1,506 scientists that served as peer reviewers in 2015. We greatly appreciate all that is done by the research community members to make this journal what it is. Thank you!


This is a photo taken at our editorial board meeting at AGU HQ in July 2014.

This is an increase of about 100 people from last year. The total number of reviews conducted was 3,592, also about 100 more than last year. We sent out 7,660 requests to review last year, which is up about 300 from last year, so our response rate dropped just slightly, down to 47%. Still, a great number, since this includes the “not needed” designation when others fill the two reviewer slots before the rest of the requests are answered. If you remove this category (1755 requests that were “not needed”), then the acceptance rate jumps up to 83%. Awesome!

A value I reported last year is the accept-to-decline ratio. There were 1884 declines, therefore this ratio is 1.9, just slightly lower than last year but still very high. Thanks for saying yes so often to our requests.

Yet another number for comparison with last year’s reviewer statistics: there were 341 times that a request was designated as “no response.” This is when the potential reviewer didn’t answer repeated requests and so we moved on to others. This is different than “not needed,” which is when other potential reviewers filled all of the desired slots before that person found time to answer. With a better than 10-to-1 ratio of acceptances to no responses, I think the community is doing very well. So, thank you, again!

Other 2015 stats from the Editorial: (a) the average number of manuscripts reviewed for each reviewer that served last year was 2.4; (b) 277 people did 4 or more reviews in 2015; (c) the total number of manuscript final decisions in 2015 was 1,147; (d) the acceptance rate was 67%; (e) there were 1,334 revision decisions; (f) on average an Editor makes 2.2 “decisions” for every assigned paper; (g) there are 3.1 reviews needed per manuscript, including reviews of revisions.

Again, thanks for all of your hard work for JGR Space Physics. We really appreciate the community support for this journal.