Three ways to improve impact factors
It’s that time of year again when the new Impact Factor values are released. This is such a big deal to a lot of folks that it’s pretty hard to avoid hearing about it. We’re not the sort of folks that object to the use of impact factors in general – we are scientists after all and part of being a scientist is quantifying things. However, if we’re going to quantify things it is incumbent upon us to try do it well and there are several things that we need to address if we are going to have faith in our measures of journal quality.
1. Stop using impact factor use Eigenfactor based metrics instead
The impact factor simply determines the number of papers that cite another paper and calculates the average. This might have been a decent approach when the IF was first invented, but it’s a terrible approach now. The problem is that according to network theory, and some important applications thereof (e.g., Google), it is also important to take into account the importance of the papers/journals that are doing the citing. Fortunately we now have metrics that do this properly: the Eigenfactor and associated Article Influence Score. These are even report by ISI right next to the IF.
Here’s a quick way to think about this. You have two papers, one that has been cited 30 times by papers that are never cited, and one that has been cited 30 times by papers that are themselves each cited 30 times. If you think the two papers are equally important, then please continue using the impact factor based metrics. If you think that the second paper is more important then please never mention the words “impact factor” again and start focusing on better approaches for quantifying the influence of nodes in a network.
2. Separate reviews (and maybe methods) from original research
We’ve known pretty much forever that reviews are cited more than original research papers, so it doesn’t make sense to compare review journals to non-review journals. While it’s easy to just say that TREE and Ecology are apples and oranges, the real problem is journals that mix reviews and original research. Since reviews are more highly cited, just changing the mix of these two article types can manipulate the impact factor. Sarah Supp and I have a paper on this is you’re interested in seeing some science and further commentary on the issue. The answer is easy, separate the analyses for review papers. It has also been suggested that methods papers have higher citation rates as well, but as I admit in my back and forth with Bob O’Hara (the relevant part of which is still awaiting moderation as I’m posting) there doesn’t seem to be any actual research on this to back it up.
3. Solve the problem of metrics that are strongly influenced by the number of papers
In the citation analysis of individual scientists there has always been the problem of how to deal with the number of papers. The total number of citations isn’t great since one way to get a large number of citations is to write a lot of not particularly valuable papers. The average number of citations per paper is probably even worse because no one would argue that a scientist who writes a single important paper and then stops publishing is contributing maximally to the progress of science.
In journal level citation analyses these two end points have up until recently been all we had, with ISI choosing to focus on the average number of citations per paper and Eigenfactor the total number of citations . The problem is that these approaches encourage gaming by journals to publish either the most or fewest papers possible. Since the issues with publishing too many papers are obvious I’ll focus on the issue of publishing too few. Assuming that journals have the ability to predict the impact of individual papers , the best way to maximize per article measures like the impact factor is to publish as few papers as possible. Adding additional papers simply dilutes the average citation rate. The problem is that by doing so the journal is choosing to have less influence on the field (by adding more, largely equivalent quality, papers) in favor of having a higher perceived impact. Think about it this way. Is a journal that publishes a total of 100 papers that are cited 5 times each, really more important than a journal that publishes 200 papers, 100 of which are cited 5 times each and 100 that are cited 4 times each? I think that the second journal is more important, and that’s why I’m glad to see that Google Scholar is focusing on the kinds of integrative metrics (like the h-index) that we use to evaluate individual researchers.
The good news is that we do have better metrics, that are available right now. The first thing that we should do is start promoting those instead of the metric that shall not be named. We should also think about improving these metrics further. If they’re worth talking about, they are worth improving. I’d love to see a combination of the network approaches in Eigenfactor with the approaches to solving the number of publications problem taken by Google. Of course, more broadly, we are already in the progress of moving away from journal level metrics and focusing more on the impact of individual papers. I personally prefer this approach and think that it’s good for science, but I’ll leave my thoughts on that for another day.
UPDATE 2: Fixed the broken link to the “Why Eigenfactor?” page.
 Both sets of metrics include both approaches with total citations from ISI and Article Influence Score, which is the per paper equivalent of the Eigen Factor, it’s just that they don’t seem to get as much… um… attention.
 And if they didn’t then all we’re measuring is how well different journals game the system plus some positive feedback where journals that are known to be highly cited garner more readers and therefore more future citations.