by PhilipJ on 9 February 2009
Physical Review Letters has traditionally been one of the top pure physics journals. Sure, Nature and Science are for exciting physics research as well, but there is something dignified and respectable about getting a Letter published in PRL. It isn’t, however, a heavy hitter in the impact factor game. As of 2008 it has a respectable impact factor of around 7, but compared to values of high 20s for Nature and Science, and the mid-to-high teens for the newcomers Nature Physics and Nature Materials, it might seem as if the PRL “brand” has suffered a little.
An editorial titled Is PRL Too Large to Have an ‘‘Impact’’? in this week’s PRL addresses some of the issues surrounding the journal and the impact factor. Not surprising to me, that single number fails to tell the whole story.
In particular, the goal of PRL is to publish “important fundamental research in all areas of physics”, and has been continually expanding its scope to include the disparate fields like biological physics that have really only emerged in the past decade. It now publishes some 4000 Letters each year, despite an increasing rejection rate.
The editorial goes on to show something like an “impact factor density” for the year 2006, or what the impact factor could be if the journal knew a priori just how many citations their articles would get, and limited the number of articles published to only those that would garner these high citations. The data point for Reviews of Modern Physics is thrown in to show what happens when you only publish 30-odd papers a year.
The “long tail” in this distribution is very long indeed: to get the impact factor for PRL up in the teens, they would have to publish approximately a fifth as many articles as they currently do. What’s also interesting, however, is that the top 500 or so PRL articles if published on their own would have an impact factor in the 20s, significantly higher than any other journal which covers just physics.
The editors at PRL had this to say about the data:
[E]ven a journal that publishes very many highly cited papers cannot achieve an impact factor above 20 in physics unless it publishes at most only a few hundred papers per year. The averaging process that the impact factor entails means that attracting even dozens of stellar papers each year will not signiﬁcantly increase the impact factor of a journal that publishes thousands of papers. Newer bibliometric measures, such as the h-index, the Eigenfactor, etc., provide different perspectives.
And what are they trying to do to improve the journal’s image?
[W]e are not about to ramp up its impact factor in the short term to, say, twice its current value. To do so would entail drastically changing the scope of what we publish. However, as noted above, each year PRL contains several hundred Letters that as a set surpasses in citations any other physics journal in the world. We hope to attract even better submissions and more readers by highlighting this set. The new online publication Physics and PRL Suggestions are signiﬁcant steps in that direction.
This is an incredibly refreshing take on the impact factor game. Obsessing about a single number from a flawed metric should never change the scope of a journal as esteemed as PRL. I only hope other editors start taking a similar stance.