Warning: astonishingly trivial
Three weeks ago I showed you my Journal Life List, and I invented the Journal Diversity Index (J/P, where my P papers have appeared in J different journals). A lot of you liked that and calculated your own JDIs, and I don’t know that we learned anything profound, but it was fun and there’s nothing wrong with that.
But I can never leave well enough alone.
A few folks pointed out that when you publish your first paper, your JDI has to be 1.0 (one paper, one journal). That’s true! A few more suggested that as a consequence, your JDI should only decline through your career. That isn’t strictly true, although it’s a tempting mistake. But it got me wondering about the temporal trend in my JDI, and since I had the data and a graphing package (not R, in case you’re wondering), off I went. Here’s the result: my JDI from the date of my 1st publication to my most recent (69th, omitting monographs, book chapters, and nonreviewed contributions). My data are in blue, bounded by the theoretical upper and lower limits in grey (1.0 and 1/P, respectively).
The overall trend in my JDI is indeed downward, but there’s more to the pattern than that. To start off, my JDI stayed at 1.0 for what seems to me a remarkably long time (through my first 13 publications*). Then the downward trend started, although it was punctuated by several apparent increasing runs. I thought those increases would be associated with shifts in my research program – I’ve had quite a few. But they aren’t; they seem to be nothing more than chance (just like most streaks in sports). Humans are really good at seeing pattern when it isn’t really there, which is why we need inferential statistics. While I haven’t done a runs test on my JDI data, I’m pretty sure one would fail to detect significant runs up or down. Finally, around publication #40, my JDI flattened out; since then it’s ticked up or down a little but stayed between 0.6 and 0.65.
That long period of JDI stasis interests me, because of the suggestion I mentioned that JDI should always trend down. Of course, if you publish enough papers, it has to. If there are about 30,000 scientific journals being published**, then once I’ve published 30,000 papers I have no choice but to repeat. In practice, of course, nobody will ever exhaust all the journals. That means the temporal movement of your JDI will reflect three factors:
- the increasing pool of journals in your discipline already on your life list, which makes it harder and harder to submit to a journal not already represented, and hence tends to push JDI down;
- the advent of new journals, which (assuming that you publish in them) tends to push JDI up; and
- your disciplinary drift, as you move to new projects in new study systems and new subdisciplines, which gives access to previously unavailable journals and so also tends to push JDI up.
OK, what have we learned today? That JDI needn’t decline monotonically; that JDI can (and I hypothesize tends to) reach a quasi-steady state, but that it takes quite a while to do so; and (mostly) that when I tag a post “Warning: astonishingly trivial”, I’m not kidding. Sorry about that.
© Stephen Heard August 29, 2017
*^Can anyone beat my record? I mean, it isn’t a competition or anything. Unless I win 🙂