There’s an interesting question about peer-review of journal articles that I’ve never seen addressed: How long does it take to review a paper? I don’t mean the three weeks or so between getting a request and submitting a review, but rather the time spent actually reviewing. In other words, how many hours does a reviewer spend reviewing the paper and not doing anything else? For myself I would guess that this is 2-3 hours for a typical paper, which includes reading and re-reading as well as writing the actual assessment. (Some papers have been considerably more time-consuming than this; few have been less.)
The question was triggered by a comment from Andrew Gelman (who writes a very good statistics blog), who states that his reviews take 15 minutes each. (!) My reviews are certainly longer than most people’s, but I find it inconceivable that I could do anything meaningful in 15 minutes. The handful of people I’ve talked to report a time of a few hours per paper. I would think that journals might have a good estimate of this, from surveys of reviewers perhaps, since it would be useful for them to know how much labor they are asking their reviewers to provide (for free). However: I asked a journal editor friend of mine, who replied that they haven’t collected any data on reviewer’s time-per-review! (I don’t know about other journals.)
Journals complain (e.g. here) that it’s hard to find willing reviewers. Reviewers complain that they get too many requests to review papers. Authors complain that reviewers are slow and capricious. Everyone complains that peer review is “broken.” Perhaps a better tabulation of what time and effort peer review requires would help address all this!
If you, dear reader, would like to comment on:
(i) how long it takes you to review a paper
(ii) how many requests to review manuscripts you get
(iii) what fraction of requests to review you accept
(iv) what field you’re in
that would be great! I’ll see if any conclusions emerge…Also, of course, it would be great to know if someone else has already done this, with the outcome available to read.
(Today’s illustration: from a card the kids and I made a few days ago.)
The Eighteenth Elephant 
I take ~2 hours. The first half hour is spent thinking, “Yep, pretty good” and then increasing despair and how horrible it actually is. I don’t think I’ve suggested accepting a paper yet this year. I review 1 paper every two months, and accept 25% of the the requests to review. I am almost always sent papers that use genotyping by sequencing.
The quick slide from optimism to despair sounds like most journal clubs I’ve been part of.
(i) how long it takes you to review a paper: between 2-4 hours
(ii) how many requests to review manuscripts you get: 5-10/year
(iii) what fraction of requests to review you accept: about 50%
(iv) what field you’re in: medieval hispanic literature/culture
This is very interesting (see also Eric’s comment below). I had no real sense of what’s involved in Humanities article review. I’m surprised how similar all your numbers are to the others, at least roughly. There’s a paper waiting to be written on Universal Laws of Article Review. (But who would review it?)
I’ll paste in a response from a friend via Facebook: “between half a work day to an entire weekend,” and a total number of 5-6 per year. (Field: biophysics.)
(i) how long it takes you to review a paper: about 3-4 hours
(ii) how many requests to review manuscripts you get: about 2 per month (24 per year)
(iii) what fraction of requests to review you accept: 90%…..I have a hard time saying no. Don’t tell the editors this!
(iv) what field you’re in: Biological Physics
(i) ~4 hours (separated into first read and second read, at least a day apart) (large standard deviation, definitely not a normal distribution)
(ii) ~8 / year but sadly peak around the same time as other demanding tasks.
(iii) ~50% – I limit my reviewing activities per month, so when I’ve got lots of grants to review, or a thesis to read, then I decline. Also, I have decided only to say yes to papers for which I am likely to learn something of direct relevance to my own research. That way, I ensure that I am capable of and interested in doing a very thorough job.
(iv) Biophysics.
Yes, I’m more likely to say yes to papers that I think I’ll learn something from — especially ones that force me to read the literature in areas I’m deficient in. Of course, if this holds in general I suppose it implies that papers are most likely to be reviewed by reviewers who aren’t quite experts in the subject!
My brother-in-law says he spends half a day, does it a few times a year, and is in German Literature.