Table 2. Approaches to peer review.

1. Open/masked peer review
Label	Author	Description from paper
Open peer review	Barroga (2020)	‘Open peer review discloses the names of the editors and reviewers handling the paper to the authors.’
Open peer review	Bruce et al. (2016)	‘“Open” peer review process, whereby peer reviewers are informed that their name would be revealed to the authors, other peer reviewers, and/or the public.’
Open peer review	Burley (2017)	‘Open peer review with signed reports that are available with the published article, where a response by the author may be included.’
Transparent peer review	Burley (2017)	‘Transparent peer review by which the unsigned review reports are made available alongside the published article, and a response by the author may be included.’
Open review	Horbach & Halffman (2018)	‘We use the term ‘open review’ merely to indicate that the identity of the authors and reviewers are mutually known to each other.’
Open peer review	Tennant (2018)	‘It has been diagnosed to refer to seven key aspects of peer review: open identities, open reports, open participation, open interaction, open pre-review manuscripts, open final-version commenting and open platforms (or ‘decoupled review’) ( Ross-Hellauer, 2017)
Open peer review	Tennant et al. (2017)	‘No agreed definition.’ Cites OpenAIRE survey which found 122 different definitions in use ( Ross-Hellauer, 2017)
Blinded/masked peer review	Bruce et al. (2016)	‘... reviewers are blinded to author names and affiliation. Author names and/or potentially identifying credentials are removed from manuscripts sent for peer review so as to remove or minimize peer reviewer biases that arise from knowledge of and assumptions about author identities.’
2. Pre/post publication review
Label	Author	Description from paper
Pre-peer review commenting	Barroga (2020); Tennant et al. (2017)	‘Pre-peer review commenting involves the informal commenting or discussion on a publicly available pre-publication manuscript draft.’
Pre-publication peer review	Barroga (2020); Tennant et al. (2017)	‘Pre-publication peer review consists of a formal and editorially invited evaluation of research by selected experts in the relevant field.’
Post-publication peer review	Barroga (2020); Tennant et al. (2017)	‘Post-publication peer review comprises a formal and optionally invited evaluation of research by selected experts in the relevant field after publication.’
Post-publication commenting	Barroga (2020); Tennant et al. (2017)	‘Post-publication commenting consists of an informal discussion of published research independent of any formal peer review.’
Post publication peer review	Horbach & Halffman (2018)	‘In these archives [pre-print servers], manuscripts usually go through a minor evaluation to check whether they meet minimal standards of academic writing. Subsequently, the actual review is done by community members who comment on the manuscript... Authors can then improve the manuscript and upload new versions to the archive.’
Post publication peer review	Burley (2017)	‘... takes place only after publication and is usually fully open.’
Registered reports	Horbach & Halffman (2018)	‘In this form of peer review, which is still restricted mainly to medical fields and psychology, manuscripts are usually reviewed in two stages. The initial and most important review stage takes place after the study has been designed, but prior to data collection.’
3. Collaboration and decoupling
Label	Author	Description from paper
Collaborative review	Barroga (2020); Tennant et al. (2017)	‘Collaborative review involves manuscript assessment wherein referees, editors, and external readers provide interactive comments leading to a consensus decision and a single set of revisions.’
Interactive peer review	Barroga (2020); Tennant et al. (2017)	‘... the reviewers interact online with the authors and other interested scientists for a more open and collaborative review.’
Discussion during review	Horbach & Halffman 2018	‘Some journals … have attempted to improve editorial decision making by introducing interactive stages in the review process, during which reviewers and editors can share or discuss their reports and opinions on a manuscript before communicating a final decision to the author’
Cascading peer review	Barroga (2020); Tennant et al. (2017)	[Using this method] … ’rejections are avoided by redirecting peer-reviewed but rejected papers to a more suitable publication venue. The consortia enable papers with the referee reports to move easily between publishers, reducing time and expense of repeated evaluation. Some pass on the peer reviews with the rejected papers. Occasionally, reviews from other journals accompanying manuscripts rejected are used for other journals.’
Cascading peer review	Horbach & Halffman (2018)	‘[This model…is now widely used, especially by larger publishing houses. The system aims to avoid final rejection of a manuscript after peer review by redirecting critically reviewed manuscripts to potentially more suitable journals.’
Cascading peer review	Burley (2017)	‘[This method]…is based on the principle of reviewing a submitted manuscript only once (if possible) and offering to the author(s) a suitable publication venue in a tiered structure.
Peer review as a separate service	Burley (2017)	‘More experiments are underway [such as] making peer review independent of the journal and providing it as a service’
Recommendation services	Barroga (2020); Tennant et al. (2017)	‘Recommendation services review involves post-publication evaluation and recommendation of significant articles, often through a peer-nominated consortium.’
Portable review	Barroga (2020); Tennant et al. (2017)	‘Portable review means the authors pay a company...for a standard single-blind review that they can submit with the paper to collaborating journals.’
Independent peer review	Barroga (2020); Tennant et al. (2017)	‘In independent peer review … a number of companies provide pre-submission peer review for a fee...Thus, reports from commercial reviewer platforms are used to assist in peer review. This involvement of commercial refereeing bodies allows the dissociation of review from the journal publishing the article, thereby facilitating a faster review (e.g., Rubriq, Peerage of Science, Axios Review) or the detection of integrity issues (e.g., Research Square). Some companies use an online “scorecard” to determine strengths and weaknesses of a paper. For Peerage of Science, the fee is paid by the journal which publishes the offering.’
Decoupled post- publication review	Barroga (2020); Tennant et al. (2017)	‘Decoupled post- publication review consists of adding notes directly to the highlighted sections of the work. These added notes can be kept private or made public.’
Review by third parties	Horbach & Halffman (2018)	‘In addition to the systems providing pre-publication review, other independent platforms have emerged... in which any reader can comment on any published manuscript. These systems constitute examples of post-publication review independent of journals and publishers. These new trends have increasingly widened the definition of a peer, so that the term now refers … to anyone who feels capable of understanding and evaluating a given piece of research.’
4. Focussed and specialised review
Label	Author	Description from paper
Soundness only review	Horbach & Halffman (2018)	‘A major development in [peer review models] … came with the launch of the open access journal PLoS ONE, by the Public Library of Science (PLoS), in 2006. In this journal’s review process and business model, reviewers are asked to base their recommendation for acceptance or rejection purely on the soundness and validity of the research, comprising the methodology, soundness of results and reporting.’
Results free review	Burley (2017)	‘Results-free review means that in a first step the paper is evaluated only for its rationale and method, not the results. If the former is deemed suitable for publication, then this is offered in principle. In a second step, the results are reviewed too. Publication may only be rejected if the results deviate unjustifiably from the stated aims and methods.’
Specialised review	Horbach & Halffman (2018)	‘Over the past decades, new actors have joined the review process, thereby compelling peer review itself to become more specialised. This applies to its content, for example introducing specialised statistical reviewers, as well as to the process ...’
Specialised review	Horbach & Halffman (2018)	‘... plagiarism detection software tool to assist in peer review, the CrossCheck system being the most common ...’ ‘Automatic analysis that checks for the correct use of statistics in manuscripts using AI.’
Specialised review	Horbach & Halffman (2018)	‘The assistance of software in detecting image manipulation, which is considered an increasing form of fraud in various research areas... it has already become possible to check for bad reporting, … data fabrication and image manipulation … usually done by … the editorial team or journal’s staff.’
Specialised review	Bruce et al. (2016)	‘Addition of peer reviewers for specific tasks or with specific expertise such as adding a statistical peer reviewer, whose main task is to detect the misuse of methods or misreporting of statistical analyses.’