In a recent commentary published in the journal Science and Engineering Ethics, José Derraik has proposed two criteria for deciding whether one should accept a peer-review invitation. Quoting directly from his article, these are

1. If a given scientist is an author in x manuscripts submitted for publication in peer-reviewed journals over y months, they must agree to peer-review at least x manuscripts over the same y months.
2. The perceived status of the journal requesting input into the peer-review process must not be the primary factor affecting the decision to accept or decline the invitation.

As a member of the editorial board of a small open-access journal that is trying to do some good in the world, BIOMATH, I fully concur with Derraik’s second point. If someone has submitted a paper in good faith to a scientific journal, and that journal is seeking expert advice on the quality of the paper, that advice should not be withheld without good reason. Prestige of the journal shouldn’t even be a consideration. I’m not talking about shady journals here, and in any event, the shady journals don’t typically look for peer reviewers.

I also have some sympathy for Derraik’s first point. We all receive too many requests to referee papers. At some point, you have to decide that you have done enough. I’m not sure about the simple equality between published papers and refereed papers that Derraik suggests. I think this is likely to lead to an undersupply of qualified referees. His argument relies on the fact that most papers have multiple authors, but at least in the fields I follow closely, most of those authors are students. While a student can co-referee a paper with a senior scientist as a training exercise, the senior scientist still has to take primary responsibility for the review. In order for the system to work properly, I suspect that most of us have to referee twice or three times as many papers as we write. The multiplier might be smaller (perhaps as small as 1) for people who write a lot of papers with many coauthors, but those folks are outliers. Nevertheless, I think Derraik is right that there has to be some proportionality between output and contribution to refereeing.

I think there’s another principle that we should add to Derraik’s list:

3. If you can’t think of very many alternative referees who are as qualified as you are to review the submission you have received, then you should accept the invitation.

This happens more often than you might think. Authors suggest referees based on the people they know in the field doing similar work. Editors similarly work hard to match the paper with appropriate referees, so it does happen fairly often that you’re the ideal referee for something you have received. In those cases, you should assume your responsibilities and do the work if it’s at all possible.

The flip side of Derraik’s list, which he doesn’t tackle directly, is the question of when you should refuse a referee assignment. To me, it comes down to a few things:

1. I do consider whether I have been doing too much refereeing lately. There is only so much time, and at some point you need to write papers rather than read other people’s stuff all the time.
2. I always ask myself if I can easily think of other qualified referees. If the answer is yes, I’m more inclined to decline the invitation. That doesn’t mean I automatically decline such invitations, only that I worry less if I feel I have to decline based on other considerations. And of course, I always pass along a list of potential referees to the journal when I do decide to decline an invitation on this basis.
3. Sometimes, you receive papers you’re just not that qualified to review. Then you should definitely turn down the invitation.
4. On occasion, you receive something and realize that other time commitments will make it impossible for you to complete the refereeing assignment in a reasonable span of time. Note that journals increasingly request a return of referee reports on unreasonable timetables. (Two weeks? Get real!) I have to admit that I sometimes turn down refereeing requests because the journal is proposing unreasonable timelines. I simply refuse to jump just because somebody says so. In other cases, I ask the editor if he/she would be willing to receive a report within x weeks, where x is a value chosen to work around other commitments, with x typically less than or equal to 4. They almost always say yes to these requests. There are times though when I’m so busy that I really could not read the paper and return the report for many, many weeks. In these cases, it’s best to decline the invitation right away.

Refereeing papers is a largely thankless job (although you may want to check out Publons, which is working to change that). That doesn’t make it less important, but it does mean that you have to balance the time you put into that against other commitments. To me, the overriding consideration is expertise: Am I the right person for the job? If the answer is yes, and you’re not completely overwhelmed with other duties, you really should accept the assignment.