  Editors are crucial to the integrity of the scientific publishing process,
yet they themselves could face conflicts of interest (COIs), whereby their
personal interests interfere with their editorial duties. One such COI stems
from the fact that, apart from a few exceptions, the vast majority of editors
are research-active scientists with many collaborators. Each such editor could
potentially handle submissions from their recent collaborators, allowing the
editor to use their power, consciously or otherwise, to treat such submissions
favourably, thereby jeopardizing the integrity of the editorial decision.
Naturally, a number of policies have been put in place to govern such COI, but
their effectiveness remains unknown. We fill this gap by analyzing half a
million papers handled by 60,000 different editors and published in 500
journals by six publishers, namely Frontiers, Hindawi, IEEE, MDPI, PLOS, and
PNAS. We find numerous papers handled by editors who collaborated recently with
the authors; this happens despite policies explicitly prohibiting such
behavior. Overall, nearly 3% of journals have a COI rate $\geq$ 10%, and nearly
half of them have a COI rate $\geq$ 2%. Moreover, leveraging three
quasi-experiments, we find that COI policies have a limited, if any, effect on
regulating this phenomenon. Finally, we find that editors are faster to accept
submissions from their collaborators, raising the possibility of favoritism.
These findings highlight the need for policy reform to assure the scientific
community that all submissions are treated equally.
