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This review reflects comments and contributions from Martyn Rittman and Stephen Gabrielson. Review synthesized by Stephen Gabrielson.

Brief summary of the study

• The authors collected preprints and journal articles, and the links between them. They considered the year of publication/posting, discipline, and country of origin and found that the number of articles with a corresponding preprint varies greatly with discipline and region. The authors also found that the adoption of preprinting depends on both of these factors, which is very interesting!

Major comments

• The omission of preprints (i.e. working papers, etc) in economics and humanities from RePec and similar repositories seems very significant and I wouldn’t rely on the results presented in those disciplines.

• While the presentation of counts and analysis are excellent, it would have been nice to know what the authors expected to see and more speculation of the probable causes, especially the effects of specific preprint servers such as arXiv and bioRxiv which dominate their respective disciplines. 

Minor comments

• In section 2.3, on matching, it would be good to preface it with a discussion that no matching method will ever be 100% complete or accurate. Would the authors be able to say what level of accuracy they would like to see achieved?

• In the last paragraph of the Limitations section, I would suggest adding a reference to medRxiv’s policy on excluding case studies, narrative reviews, etc. Are there also times that clinical studies and studies on drug therapies could not be preprinted?

• In section 5.1, I wonder if journal policies in the health sciences have also changed since the pandemic to allow authors to submit preprinted work and also reference preprints in their peer-reviewed manuscripts? And if this influenced an author to post a preprint? Was this discussed in any of the literature the authors referenced?

Comments on reporting

• In section 3.1, Step 2, could the authors not have used information in the data, e.g. identified relationships between versions?

Suggestions for future studies

• Mathematics and physical sciences are dominated by arXiv and see large disparities in adoption between regions. Do the authors think there might be a connection, for example a culture of using arXiv to find research, access to the platform, or the requirement for endorsement to post a preprint on arXiv? 

• Do the authors see general patterns in how preprints in a specific discipline or region develop, e.g. periods of fast development triggered by specific events such as establishing a discipline-specific preprint server or COVID.

Conflicts of interest of reviewers

• No conflicts of interest to report.

Competing interests

The authors declare that they have no competing interests.