Which peer reviewers voluntarily reveal their identity to authors? Insights into the consequences of open-identities peer review

Identifying reviewers is argued to improve the quality and fairness of peer review, but is generally disfavoured by reviewers. To gain some insight into the factors that influence when reviewers are willing to have their identity revealed, I examined which reviewers voluntarily reveal their identities to authors at the journal Functional Ecology, at which reviewer identities are confidential unless reviewers sign their comments to authors. I found that 5.6% of reviewers signed their comments to authors. This proportion increased slightly over time, from 4.4% in 2003-2005 to 6.7% in 2013-2015. Male reviewers were 1.8 times more likely to sign their comments to authors than were female reviewers, and this difference persisted over time. Few reviewers signed all of their reviews; reviewers were more likely to sign their reviews when their rating of the manuscript was more positive, and papers that had at least one signed review were more likely to be invited for revision. Signed reviews were, on average, longer and recommended more references to authors. My analyses cannot distinguish cause and effect for the patterns observed, but my results suggest that 'open-identities' review, in which reviewers are not permitted to be anonymous, will probably reduce the degree to which reviewers are critical in their assessment of manuscripts and will differentially affect recruitment of male and female reviewers, negatively affecting the diversity of reviewers recruited by journals.