Seeing as I'm still deep in the paper production time, I've been thinking a lot about whether there is an optimal number of figures, and if so, what that number might be. Then Dr. Jekyll + Mrs. Hyde got the ball rolling in wondering why seven figures seems to be the norm. Also, we've probably all heard the anecdote that as the number of figures in a paper increases, the number of people who read it decrease.
I think that the number of figures per se is not terribly meaningful. Unless there are journal dependent requirements (think GlamourMagz), then a paper should have as many figures as are needed to tell the story. If that's 5 figures, good. If that's 15 figures, so be it.
But what's important to me is that each figure contains a coherent point*, conveys that point as succinctly as possible, while still reflecting the reality of the result.
What really gets all up in my grill is when people cram panels into a set number of figures, while blending the points together. That's one way to fit into an external figure limit, while increasing the amount of data presented. I think it fails because it dilutes the take home message from each figure. Also, it destroys any visuo-cognitive impact a figure has. When I look at a figure, I want to be able to see that message almost immediately, and preferably without referring to the legend. When I have to go through each of A-J panels, that ain't gonna happen.
So as a little test, I quickly went through 15 pdfs that were in my "PapersToSummarize" folder, and looked at the total number of figures, as well as the total number of panels in each figure. What struck me was that regardless of the total number of figures, the total number of panels was actually not that different. Now, this is a completely non-random sample, and reflects mostly electrophysiology related papers, with only a smattering of GlamourMagz, but let's look:
Ok, so the median number of figures was 7, perhaps reflecting DrJ+MrsH's impression that 7 is heaven. But also, it's pretty clear that regardless of total number of figures, right about 29-35 panels (overall avg was 32 panels). So those people who don't read a paper with too many figures (if they even exist) are deluding themselves in thinking that really means anything. See, here's a graph to prove it (and they say there's no science on science blogs. There's goddamn regression line in there. You call that no science?):
See, there ya go. Papers with more figures have more panels, but the slope is only ~2 panels/figure. Also, extrapolating to zero figures gives us the predicted absolute minimum panels for a zero figure paper, ~20. Anyway though, the correlation is crap here, with R-squared 0.21.
After doing this, I decided to check back on my papers from my thesis lab, since as those were two author papers, I did the lion's share in planning the figures and their layouts (I'll include the albatross around my neck, one manuscript that will, will see the light of day, even if I have to drown a couple hundred crewmen to publish it; it'll make for a kick ass song though):
11 figures, 27 panels, for 2.5 panel/fig.
11 figs, 27 panels, 2.5
10 figs, 29 panels, 2.9
And the number of panels ranged from 1-5. Pretty consistent.
So readers, tell me: What is your ideal number of figures?
*by point here i mean someting like a quantum of scientific result. Yeah, I just made it up, but maybe other people intuitively understand it.