While glancing through journal metrics recently for some of the most well known mathematical biology journals (with a bias towards ecology), I noticed something a bit disturbing. It appears that theoretical papers are declining in citations. Basically, the number of citations per article has been decreasing over the past 4-years in nearly every well respected theoretical biology journal I could think of. Some of the declines may not be statistically significant, but as a whole, the trend seems pretty clear (see the middle time-series plot in each of the graphs below – labeled “cites per doc” – from scimago).
The above journals range in how “theoretical” they are. Some might argue that the first three aren’t really theory journals at all, but I left them up there anyway since they are theory friendly journals.
I have three alternative hypotheses for the downward trend in per article citation
- Scientists have started to avoid reading/citing pure theory in biology
- The best and most influential theoreticians now team up with empiricists to publish high impact science papers, this means some of the best ideas, that would have gone to theory journals in the past, are now components of papers in Science, Nature, & other more general biology journals. In other words, data is being used to test some of the most promising ideas and the leftover ideas that couldn’t be tested against data go to the theory journals.
- Citations per article might be declining in biology in general, and hence the decline in theoretical biology is expected. This might be explained by something like the mean length of reference lists declining (possibly due to journal page limits or increased motivations to publish short zippy letter style papers)
Or perhaps it’s a combination of all three of these. Looking at some top ecology and general biology journals (below) it seems like hypothesis three might be the most likely. Cell, TREE, and Ecology Letters all seem to be declining. So it isn’t that the top journals are eating up all the citations of lower ranked journals. One might think that with an increasing number of articles published each year, that perhaps the top papers benefit the most from this (given how citations tend to be distributed), but this doesn’t seem to be the case, as far as I can tell.
I’m not so sure how general journals (outside of biology) stack up on this list, so maybe it is that biology journals are being cited less. I’m not so sure what to make of this. What do you think might be the cause of the perhaps general downward trend of cites/article? Or maybe it isn’t a trend at all, and this is all happening just by chance? I haven’t done any statistics to back anything I said up so it would be interesting to get a hold of some raw data (which scimago, doesn’t seem to share online) and analyse these hypotheses a bit more rigorously. Feel free to discuss in the comments.
Jeremy Fox has written quite a bit about theory and its value (and perceived value) in ecology, see the following:
Should theory published in general ecology journals have to be realistic? especially see Brian McGill’s comment, which might be considered an alternative hypothesis to the ones above. He basically argues that simple, general models might be for the most part fully explored, and hence the majority of what is left in theory journals these days is complex models, which aren’t so general. Complex models for specific situations should probably involve some data. If I were to continue Brian’s logic, if theory journals are now publishing more data-free complex model papers, they might be deservedly uncited.