An Update on the AAS Journals' Impact Factors
Here's some good news from AAS Publishing: The impact factors of three of our peer-reviewed journals have increased over the last year, two of them by a lot. Leading the pack is the Astrophysical Journal Letters (ApJL), whose impact factor jumped 26% from 6.634 in 2017 to 8.374 in 2018 — the highest it's ever been. This surely reflects the Society's renewed dedication to ApJL's mission of rapidly publishing articles of great interest and great significance to the astronomical community. Another likely factor is the introduction of "focus issues" featuring collections of papers on special topics, such as the first direct detection of gravitational waves and the first image of a black hole.
In case you're new to the impact factor, it's one of several quantitative tools used to evaluate journal quality. It measures the frequency with which the average article has been cited during a particular period. Compiled annually for nearly 12,000 journals by Clarivate Analytics' Web of Science Group, the impact factor is calculated by dividing the number of citations in the most recent full year to the articles published in that journal during the previous two years. So, using the numbers above, in 2017 the average ApJL article from 2015-2016 was cited 6.634 times, and in 2018 the average ApJL article from 2016-2017 was cited 8.374 times.
The Astronomical Journal (AJ) netted an even bigger fractional gain in impact factor last year, up 32% from 4.150 to 5.497. That puts it essentially equal to the 2018 Astrophysical Journal (ApJ) impact factor of 5.580, which is ever-so-slightly higher than the previous year's value of 5.551. This is just what we were hoping would happen when we introduced topical corridors to our article-submission process. Now, instead of selecting which AAS journal to submit your article to, you choose the appropriate topical corridor, and our editorial team decides which journal best suits it. ApJ's impact factor has held steady since the change, and now AJ's has increased substantially to nearly the same value as ApJ.
The other member of the ApJ family, the Supplement Series (ApJS), saw a 3% decrease in impact factor from 8.561 to 8.311 from 2017 to 2018 — still quite high, but now just below ApJL. We think the slight decline occurred because ApJS publishes fewer (and generally longer and/or more data-intensive) articles than our other journals, such that the presence (or absence) of a small number of highly cited papers can skew the impact factor up or down.
To put these numbers in context, both Science and Nature have impact factors over 40 for 2018, whereas Astronomy & Astrophysics is at 6.209, Monthly Notices of the Royal Astronomical Society is at 5.231, and Publications of the Astronomical Society of the Pacific is at 3.470. Thus, within the astronomical sciences, the AAS journals are solidly at or near the head of the pack.
AAS Publishing would like to take this opportunity to thank our journals' readers, authors, and reviewers, as well as our hard-working team of editors. Together we continue to support the AAS mission to enhance and share humanity's scientific understanding of the universe.
— The AAS Publishing Team