Conflict of Interest in Peer Review

A conflict of interest in peer review is any relationship, financial or personal, that could reasonably be expected to bias a reviewer's judgement of a manuscript, or that would appear to a neutral observer to do so. Two things follow from that definition and both are routinely misunderstood. A conflict does not require that bias actually occurred: the standard is whether the relationship could reasonably create the appearance of it, which is why declaration matters more than intention. And a conflict is not an accusation of misconduct: disclosing one is the correct, unremarkable behaviour, while failing to disclose one is the thing that becomes an integrity matter.

The test is reasonable appearance to an outside observer, not the reviewer's own confidence in their impartiality.

Declaring a relationship transfers the decision to the editor, which is where publisher policies place it.

A conflict can exist without anyone doing anything wrong, and usually does.

The obligation runs both ways

authors declare competing interests about their work, reviewers declare relationships with the authors.

The largest category, and the one that disqualifies most candidates from a suggested reviewer list. These are relationships between people rather than interests in an outcome.

Recent co-authorship

COPE guidance treats recent collaborators as conflicted, and applies a three-year window to close collaborators. MDPI asks that proposed referees have not published with any co-author in the last three years.

Supervision, in either direction

a doctoral or postdoctoral supervisor and their former students. COPE names mentors and mentees explicitly. Most policies apply no time limit to this one.

Shared institution

the same university, department, research centre or hospital group as any author. Excluded almost everywhere, and it usually still applies for a period after someone moves.

Joint grant holders and consortium partners, whether or not they have published together, because shared funding creates a shared interest in the results.

Close personal relationships

family, partners, and documented personal disputes. A disagreement in print is not one of these.

Less common in academic submissions and more serious when present, because these are interests in the outcome rather than relationships with the people.

Employment or consultancy with a company whose product, service or patent the paper evaluates.

Equity, patents or royalties whose value depends on the finding being confirmed or refuted.

Grant funding from a body with a declared position on the question, which is a disclosure rather than an automatic exclusion.

Direct scientific competition

a group racing the authors to the same result, where the reviewer would gain from a delay. This is the standard reason authors use the excluded reviewers field.

Editorial roles

an editor handling a paper from their own group steps aside, which is why journals log which editor handled which submission.

Most disputes are about when a past relationship stops counting, and the answer is set by the journal rather than by a universal rule. Where a window is stated, three years is the figure that recurs.

Co-authorship

three years is the common figure. COPE uses it for close collaborators and MDPI applies it to proposed referees.

Supervision

usually treated as permanent, or at least far longer than the co-authorship window, in both directions.

Shared institution

current, and typically extended for a stated period after a move rather than ending on the last day of employment.

Financial interests

usually a declaration covering the last several years plus anything current, with the exact period set in the journal's policy.

When a policy states no window, assume the relationship counts and disclose it. The cost of an unnecessary disclosure is nothing; the cost of an undisclosed conflict is an editorial investigation.

Editors do not take a suggested reviewer list on trust, and the checks are quicker than most authors assume. Knowing what they are is the fastest way to stop submitting names that will be discarded.

A co-authorship search on each suggested name against the full author list, which most bibliographic databases return in seconds.

An affiliation comparison against every author affiliation on the submission, including secondary affiliations.

Verification of the email domain against the stated institution, which is the check that catches fabricated reviewer identities.

The reviewer's own declaration at the point of invitation

submission systems ask the invited referee to confirm no conflict before they accept, so a candidate you should not have named will usually remove themselves.

The acknowledgements and funding statements of your own manuscript, which sometimes disclose a relationship the author list does not.

Over-application of the rules is its own problem, because it removes exactly the people who could review the paper properly. None of the following disqualifies a reviewer on its own.

Having met at a conference, or being on friendly terms without a working relationship.

Working on the same topic. That is expertise, and it is the whole point of peer review.

Having cited the authors, or being cited by them, without co-authorship.

Having publicly disagreed with the authors' conclusions in the literature. Scientific disagreement is a reason to read carefully, not a disqualification.

Having read the paper as a preprint or heard it presented at a conference. That is worth mentioning to the editor, but it is not a conflict.