For the frequencies of imposition of unnecessary references by reviewers, 67.6% (95% CI: 65.1% to 70.1%) reported rare or infrequent occurrences (see Figure 4).
Female academics, experience of personal attacks and imposition of unnecessary references by reviewers were related to disagreement about fairness of the peer review system of biomedical journals.
It is not surprising because the frequencies of non-native English-speaking respondents encountering personal attacks and imposition of unnecessary references were higher compared to native respondents.
The female gender, frequency of encountering personal attacks in reviewers' comments and frequency of imposition of unnecessary references by reviewers are the most significant factors associated with disagreement that biomedical journal peer review is fair.
We further performed multivariate ordinal regression using the three variables (female gender, frequency of encountering personal attacks in reviewers' comments and frequency of imposition of unnecessary references by reviewers) as covariates but could not find a suitable multivariate regression model.
While it is difficult to define unnecessary references, reviewers should try to avoid imposing upon authors to quote the reviewers own publications as it could lead to potential COI.
For undesirable experiences, the proportion of non-native English-speaking respondents reporting frequent occurrence of personal attacks (χ = 11.0, p = 0.004) and imposition of unnecessary references (χ = 363.4, p = 0.01) was significantly higher than that among native English-speaking respondents.
A possible explanation for this result is that the proportion of basic scientists and clinician-scientists who reported the occurrence of peer review misconduct such as personal attacks and imposition of unnecessary references was significantly higher than clinicians.
Nevertheless, frequency of encountering personal attacks in reviewers' comments and frequency of imposition of unnecessary references by reviewers were significant factors associated with perception of unfairness in journal peer review.
Among them, 11.3% (95% CI: 9.6% to 13.0%) frequently encountered peer review processes longer than 6 months, and 7.2%, (95% CI: 5.8% to 8.5%) frequently encountered imposition of unnecessary references by reviewers.
