Having analyzed 500 days of MB edits, these variables both appear to have a WikiPedia:Log-normal_distribution: most PeerReview periods involve very few edits, but there are some rare occasions when everyone wants to have a say, or two people get into a heated discussion.
Some good take-home statistics:
The graphs shown plot the logarithm of the number of (edits/edit chains) against inverse-normal of the cumulative probability; a best-fit straight line demonstrates a reasonable fit with the suggested distribution. In both cases, the SandBox is a wild extremity, not shown on the graph to avoid squashing the other points into a corner. -- ChrisPurcell
I can't remember where I found the idea, but I've been doing this kind of thing for a couple of years now. Try googling for "fitting normal distributions with gnuplot" or something, and you'll probably find the very page I used. -- ChrisPurcell
After discovering the excellent RLanguage recently, I've returned to the kind of distribution shown above. As you may have spotted, the distribution, cannot actually be log-normal (though it has a similar cumulative distribution shape) because it takes discrete values. A better distribution appears to be the lesser-known Poisson lognormal (or Discrete lognormal).
When I say lesser-known, I mean it; there is not even a WikiPedia page. Some interesting material can be found, e.g. in [Colwell] and Coddington 1994 p. 108, or [Software defect rediscoveries: a discrete lognormal model]. There is also a [poilog package for R], which gives graphs looking very like those above. However, I am loathe to claim the curve above is a discrete lognormal without further investigation. One unfortunate issue holding me back is that I have lost the data I used originally. -- ChrisPurcell