Some journals ask authors for a list of possible reviewers, and some also ask for a list of reviewers to avoid. Are these lists useful to editors? Who should be on these lists? If someone is listed as a person who should not be asked for a review, can the editor still ask that person for a review?
In my experience, these lists are advisory only. They are suggestions of some people with the necessary expertise to review the manuscript. If the author has particular opinions about issues other than expertise (e.g., objectivity), these may also be a factor in deciding which individuals to list as preferred reviewers and which, if any, to request not be asked to review.
If authors list the obvious reviewers, I have no problem picking at least one from their list of suggested reviewers, maybe even two if that makes sense and I would have asked these people anyway. In most cases, though, I try to find at least one reviewer who is not listed. If you want to increase the chances that a certain expert person will be selected, a possibly good strategy is to leave that name off your list. Whether this strategy is good or not depends on the editor's editorial habits. You may well not be aware of what these are, so in fact probably the best strategy, if required to provide a list of suggestions, is to make a sincere list of expert people.
As an editor, if I don't think the list of suggested reviewers is reasonable, I may not select any from the list. Some authors seem to believe that the editor will or must pick from their list, and they stack the list with their close colleagues and friends in their own department. This is not a good strategy because (1) it probably won't work; and (2) why give the editor reason to question your judgment and ethics?
There are certain research topics that involve feuding research groups, and the authors in each group believe (in some cases with justification) that those in the other group(s) will not give an objective review. These groups always list those in the other(s) in the do-not-review column. If I know something about the debate and the people involved, I either respect this request or I don't, depending on the people and the situation. In most cases, however, I respect the list, but if I do happen to select a reviewer from the do-not-review request list, I remain alert (as always) for any possible problems with the review, including apparently unsupported negative criticisms or what seem to me to be overly harsh reviews of matters for debate (as opposed to problems with the data or observations).
Reviewers do not decide whether a manuscript is accepted or rejected; they make recommendations. The editor decides whether the reviews are reasonable and makes the decisions, so a negative review may not be fatal.
The manuscript management system with which I am most familiar makes it very clear what author preferences are in terms of reviewers to select or avoid. Not long ago, however, I was a guest editor for a journal that used a different system, and I found this other system difficult to navigate. At first I didn't even see that there was a place for authors to list their reviewer preferences; the list was rather hidden. Also, the journal had an inefficient system for selecting reviewers for manuscripts in guest-edited issues, so I was unable to select reviewers directly. For two different manuscripts, reviewers who were on the authors' lists of reviewers to avoid were in fact asked to review the manuscripts. Both returned very constructive, overall positive reviews in which each also made their identity obvious to the authors.
In one case, the authors were enraged that a reviewer had been selected against their recommendations. They complained to the main editor. They wrote a rather nasty letter to me. This was puzzling because the reviewer gave them a very useful and positive review; there was absolutely nothing in that review that indicated a problem with objectivity. Did they just dislike on principle the fact that this person had been allowed to give input? There was nothing time sensitive in their manuscript; nothing that needed to be kept secret from certain people in advance of publication; nothing even very controversial. In fact, it was a solid but rather prosaic paper that I spent a huge amount of time editing because the writing was so bad. The authors were in error to believe that just by listing the objectionable person on a list meant that the editors were bound to comply. I probably would have respected their wishes had I known them and had I ultimate control over reviewer selection, but I was not compelled to do so.
In the other case, the authors were pleased that they had gotten such a positive review from someone they feared would not be objective. They later started corresponding with the reviewer about their mutual research interests, and sent a nice thank you letter commending the editorial work of my colleagues and me.
Some journals ask for a reason why an individual is included on a to-be-avoided list of reviewers; some funding agencies request this information as well. If there is a reasonable explanation for why an individual should not review a manuscript, then an editor may be more inclined to comply with this request.
It can be difficult to explain some of these reasons, though. Unless you are an established researcher with a long track record of publishing, you probably don't want to write "This person hates all of my papers and always gives a negative review" because it raises the question of whether all of your papers are really bad. Something vague like "conflict of interest", however, is an all-purpose, vague-but-possibly-effective reason, should you be required to provide one.
Are these lists useful to editors? Yes and no. Not really. Sort of.
Who should be on these lists? People with expertise. People who are not your close friends and colleagues.
If someone is listed as a person who should not be asked for a review, can the editor still ask that person for a review? Yes.
7 months ago