Guidelines for Reviewers

“We are sincerely grateful to scholars who give their time to peer-review articles submitted to MDPI journals. Rigorous peer-review is the corner-stone of high quality academic publishing.”
— The MDPI editorial team.

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Reviewers Guide

• 1.  Peer Review and Editorial Procedure
• 2.  Reviewers’ Profile and Responsibilities
• 3.  Reviewers’ Benefits
• 4.  Reviewer Board
• 5.  Volunteer Reviewer Board
• 6.  General Guideline for MDPI Reviewers Recruiting Program
• 7.  General Guidelines for Reviewers
•   7.1. Invitation to Review
•   7.2. Potential Conflicts of Interest
•   7.3. Declaration of Confidentiality
•   7.4. Review Reports
•   7.5. Rating the Manuscript
•   7.6. Overall Recommendation
•   7.7. Guidelines for Reviewers for Registered Reports Papers
•   7.8. Guidelines for Reviewers for Depositing Review Activities into ORCID

1. Peer Review and Editorial Procedure

Peer review is an essential part of the publication process and it ensures that MDPI maintains the highest quality standards for its published papers. All manuscripts submitted to our journals are strictly and thoroughly peer-reviewed by experts.

Immediately after submission, the journal’s Managing Editor will perform an initial check of the manuscript. A suitable academic editor will be notified of the submission and invited to check the manuscript and recommend reviewers. Academic editors can decide to continue with the peer review process, reject a manuscript, or request revisions before peer-review. In the case of continuing the peer review process, the Editorial Office will organize the peer review, which is performed by independent experts, and collect at least two review reports per manuscript. We ask authors for sufficient revisions (with a second round of peer review, when necessary) before a final decision is made. The final decision is made by an academic editor (usually the Editor-in-Chief/Editorial Board Member of a journal or the Guest Editor of a Special Issue). Accepted manuscripts are then copy-edited and English-edited internally. More details about the editorial process can be found here.

2. Reviewers’ Profile and Responsibilities

The role of the reviewer is vital and bears a great responsibility in ensuring the integrity of the scholarly record. Every reviewer is expected to perform manuscript evaluation in a timely, transparent, and ethical manner, following the COPE guidelines https://publicationethics.org/files/cope-ethical-guidelines-peer-reviewers-v2_0.pdf.

Reviewers should meet the following criteria:

• hold a Ph.D. (or MD for medical fields), preferably with postdoctoral experience;
• be an active researcher;
• possess official and recognized affiliation (University or Research Institute) relevant experience and have a proven publication record in the field of the submitted paper (Scopus, ORCID);
• not hold any conflicts of interest with the authors, including if they have published together in the last five years.

MDPI strives for a rigorous peer review to ensure a thorough evaluation of each manuscript—this is a fundamental task for our reviewers. Reviewers who accept to review a manuscript are expected to:

• Have the necessary expertise to judge the scientific quality of the manuscript;
• Provide quality review reports and remain responsive throughout the peer review process;
• Maintain standards of professionalism and ethics.

3. Reviewers’ Benefits

Reviewing is often an unseen and unrewarded task, despite being crucial. We are striving to recognize the efforts of all our reviewers.

Reviewing for MDPI journals brings the following benefits:

• For every manuscript reviewed, the reviewer may receive a discount voucher code entitling them to a reduction in the article processing charge (APC) of a future submission to any MDPI journal. The vouchers are linked to the reviewer’s email address and can be applied online during the submission or at any time before the manuscript is accepted. Note that vouchers cannot be used after an invoice has been issued, which occurs at acceptance. If your article is rejected, the voucher can instead be used for your next submission.
• The reviewers receive a personalized reviewer certificate.
• The reviewers are eligible to be considered for the “Outstanding Reviewer Awards”.
• The reviewers are included in the journal’s annual acknowledgment of reviewers if more than 50 reviewers assisted the journal in the previous year.
• Excellent reviewers may be promoted to Reviewer Board Members (subject to approval by the Editor-in-Chief).
• Reviewers may create a profile on Publons and have their reviewing activity automatically added for participating journals. Profiles on Publons can also be integrated with ORCID.

4. Reviewer Board

The Reviewer Board (RB) consists of experienced researchers whose main responsibility is to regularly and actively support journals by providing high quality, rigorous, and transparent review reports for submitted manuscripts within their area of expertise. The initial term is for 1 year which can then be renewed or terminated. Membership involves the same responsibilities and benefits as regular reviewers, with the addition of:

1. RB Members must review a minimum of 6 manuscripts per year. Should the reviewer be unable to provide a report when invited, they are expected to suggest alternative potential reviewers (the proposed candidates must meet the reviewers’ requirements from Section 2).
2. RB Members are entitled to publish one paper per year with a discount of 200 CHF (once accepted for publication after peer-review). This discount can be combined with reviewer’ vouchers.
3. RB Members are entitled to receive an RB certificate.
4. RB Members are announced on the journal website.
5. Active RB members may be promoted to the Topical Advisory Panel (subject to approval by the Editor-in-Chief).

5. Volunteer Reviewer Board

MDPI journals are actively looking for volunteers to join our Volunteer Reviewer Board. The members of MDPI’s Reviewer Board and Volunteer Reviewer Board can actively offer to review manuscripts in one or more of MDPI’s journals.

To become part of this program, you have to fulfil the criteria outlined in Section 2 entitled “Reviewers’ Profile and Responsibilities”.

To become a member of this program, please apply here: The editorial office of the selected journal will be notified. Your application will be reviewed by our internal staff, who will check if your background suits the scope of the journal as well as any potential ethical issues. Should you pass our internal check, your application will be approved.

Active members of the Volunteer Reviewer Board may be promoted to Reviewer Board Members (subject to approval by the Editor-in-Chief).

6. General Guideline for MDPI Reviewers Recruiting Program

To apply to review a manuscript, you as the Reviewers’ Board and Volunteer Reviewer Board member can visit the “Recruiting Reviewers” menu in our Submission System (SuSy) (https://susy.mdpi.com/reviewer/list/recruiting_reviewers_manuscripts). You will find this menu on the left-hand side under “Reviewers Menu”. Here you can see all the manuscripts that you can apply for*. You can search by Journal and keyword. Should you find an interesting manuscript that you would like to review, please click on “Apply”. The Editorial Office of the respective journal will be notified about your application. Our internal staff will check your research background and any potential conflicts of interest. Should you pass, your application to review will be approved.

* Please note that you can only see and apply to manuscripts in journals where you are a member of the Reviewers Board or Volunteer Reviewers Board.

7. General Guidelines for Reviewers

7.1. Invitation to Review

Manuscripts submitted to MDPI journals are reviewed by at least two experts, who can be volunteer reviewers, members of the Reviewer Board or reviewers suggested by the academic editor during the preliminary check. Reviewers are asked to evaluate the quality of the manuscript and to provide a recommendation to the external editor on whether a manuscript should be accepted, requires revisions, or should be rejected.

We ask invited reviewers to:

• accept or decline any invitations as soon as possible (based on the manuscript title and abstract);
• suggest alternative reviewers if an invitation must be declined;
• request a deadline extension as soon as possible in case more time is required to provide a comprehensive report.

7.2. Potential Conflicts of Interest

We ask reviewers to declare any potential conflicts of interest and email the journal Editorial Office if they are unsure if something constitutes a potential conflict of interest. Possible conflicts of interest include (but are not limited to):

• Reviewer works in the same institute as one of the authors;
• Reviewer is a co-author, collaborator, joint grant holder, or has any other academic link, with any of the authors within the past five years;
• Reviewer has a close personal relationship, rivalry or antipathy to any of the authors;
• Reviewer may in any way gain or lose financially from publication of the paper;
• Reviewer has any other non-financial conflicts of interests (political, personal, religious, ideological, academic, intellectual, commercial or any other) with any of the authors.

Reviewers should disclose any conflicts of interest that may be perceived as bias for or against the paper or authors.

Please kindly note that if reviewers are asked to assess a manuscript they previously reviewed for another journal, this is not considered to be a conflict of interest. In this case, reviewers should feel free to let the Editorial Office know if the manuscript has been improved or not compared to the previous version.

Reviewers are also recommended to read the relevant descriptions in the Ethical Guidelines For Peer Reviewers by the Committee On Publication Ethics’ (COPE).

7.3. Declaration of Confidentiality

MDPI journals operate single- or double-blind peer review (https://www.mdpi.com/editorial_process). Until the article is published, reviewers should keep the content of the manuscript, including the Abstract, confidential. Reviewers should also be careful not to reveal their identity to the authors, either in their comments or in metadata for reports submitted in Microsoft Word or PDF format. Reviewers must inform the Editorial Office if they would like a colleague to complete the review on their behalf (reviewers should always meet the criteria reported in Section 2).

MDPI journals offer the possibility for authors to publish review reports together with their paper (Open Review) and for reviewers to sign their open review reports once “Open Review” (https://www.mdpi.com/editorial_process) is selected by the authors. However, this will only be done at publication with the reviewer’s permission. In all other cases, review reports are considered confidential and will only be disclosed with the explicit permission of the reviewer.

7.4. Review Reports

We have listed some general instructions regarding the review report for your consideration below.

To begin with, please consider the following guidelines:

• Read the whole article as well as the supplementary material, if there is any, paying close attention to the figures, tables, data, and methods.
• Your report should critically analyze the article as a whole but also specific sections and the key concepts presented in the article.
• Please ensure your comments are detailed so that the authors may correctly understand and address the points you raise.
• Reviewers must not recommend citation of work by themselves, close colleagues, another author, or the journal when it is not clearly necessary to improve the quality of the manuscript under review.
• Reviewers must not recommend excessive citation of their work (self-citations), another author’s work (honorary citations) or articles from the journal where the manuscript was submitted as a means of increasing the citations of the reviewer/authors/journal. You can provide references as needed, but they must clearly improve the quality of the manuscript under review.
• Please maintain a neutral tone and focus on providing constructive criticism that will help the authors improve their work. Derogatory comments will not be tolerated.

Note that MDPI journals follow several standards and guidelines, including those from the ICMJE (medical journals), CONSORT (trial reporting), TOP (data transparency and openness), PRISMA (systematic reviews and meta-analyses) and ARRIVE (reporting of in vivo experiments). See the Publishing Standards and Guidelines page or contact the Editorial Office for more details. Reviewers that are familiar with the guidelines should report any concerns they have about their implementation.

For further guidance on writing a critical review, please refer to the following documents:

1. COPE Ethical Guidelines for Peer Reviewers. Committee on Publication Ethics. Available online.
2. Hames, I. Peer Review and Manuscript Management in Scientific Journals: Guidelines for Good Practice. Wiley-Blackwell: Oxford, UK, 2007.
3. Writing a journal article review. Australian National University: Canberra, Australia, 2010. Available online.
4. Golash-Boza, T. How to write a peer review for an academic journal: Six steps from start to finish. Available online.

Review reports should contain the following:

• A brief summary (one short paragraph) outlining the aim of the paper, its main contributions and strengths.
• General concept comments
  Article: highlighting areas of weakness, the testability of the hypothesis, methodological inaccuracies, missing controls, etc.
  Review: commenting on the completeness of the review topic covered, the relevance of the review topic, the gap in knowledge identified, the appropriateness of references, etc.
  These comments are focused on the scientific content of the manuscript and should be specific enough for the authors to be able to respond.
• Specific comments referring to line numbers, tables or figures that point out inaccuracies within the text or sentences that are unclear. These comments should also focus on the scientific content and not on spelling, formatting or English language problems, as these can be addressed at a later stage by our internal staff.

General questions to help guide your review report for research articles:

• Is the manuscript clear, relevant for the field and presented in a well-structured manner? 
• Are the cited references mostly recent publications (within the last 5 years) and relevant? Does it include an excessive number of self-citations?
• Is the manuscript scientifically sound and is the experimental design appropriate to test the hypothesis?
• Are the manuscript’s results reproducible based on the details given in the methods section?
• Are the figures/tables/images/schemes appropriate? Do they properly show the data? Are they easy to interpret and understand? Is the data interpreted appropriately and consistently throughout the manuscript? Please include details regarding the statistical analysis or data acquired from specific databases.
• Are the conclusions consistent with the evidence and arguments presented?
• Please evaluate the ethics statements and data availability statements to ensure they are adequate.

General questions to help guide your review report for review articles:

• Is the review clear, comprehensive and of relevance to the field? Is a gap in knowledge identified?
• Was a similar review published recently and, if yes, is this current review still relevant and of interest to the scientific community?
• Are the cited references mostly recent publications (within the last 5 years) and relevant? Are any relevant citations omitted? Does it include an excessive number of self-citations?
• Are the statements and conclusions drawn coherent and supported by the listed citations?
• Are the figures/tables/images/schemes appropriate? Do they properly show the data? Are they easy to interpret and understand?

The content of your review report will be rated by an Academic Editor from a scientific point of view as well as general usefulness to the improvement of the manuscript. The overall grading results will be used as a reference for potential promotion of Reviewer Board Members, Volunteer Reviewer Board members and regular Reviewers.

7.5. Rating the Manuscript

During the manuscript evaluation, please rate the following aspects:

• Novelty: Is the question original and well-defined? Do the results provide an advancement of the current knowledge?
• Scope: Does the work fit the journal scope*?
• Significance: Are the results interpreted appropriately? Are they significant? Are all conclusions justified and supported by the results? Are hypotheses carefully identified as such?
• Quality: Is the article written in an appropriate way? Are the data and analyses presented appropriately? Are the highest standards for presentation of the results used?
• Scientific Soundness: Is the study correctly designed and technically sound? Are the analyses performed with the highest technical standards? Is the data robust enough to draw conclusions? Are the methods, tools, software, and reagents described with sufficient details to allow another researcher to reproduce the results? Is the raw data available and correct (where applicable)?
• Interest to the Readers: Are the conclusions interesting for the readership of the journal? Will the paper attract a wide readership, or be of interest only to a limited number of people? (Please see the Aims and Scope of the journal.)
• Overall Merit: Is there an overall benefit to publishing this work? Does the work advance the current knowledge? Do the authors address an important long-standing question with smart experiments? Do the authors present a negative result of a valid scientific hypothesis?
• English Level: Is the English language appropriate and understandable?

*At this stage reviewers can also suggest that a manuscript may be more appropriate for publication in another MDPI journal. To save the time and effort of reviewers, authors have the possibility to request the transfer of review reports to another MDPI journal. The full list of journals published by MDPI can be found here.

Manuscripts submitted to MDPI journals should meet the highest standards of publication ethics:

• Manuscripts should only report results that have not been submitted or published before, even in part.
• Manuscripts must be original and should not reuse text from another source without appropriate citation.
• The studies reported should have been carried out in accordance with generally accepted ethical research standards.

If the reviewer becomes aware of any scientific misconduct or fraud, plagiarism or any other unethical behavior related to the manuscript, they should raise these concerns with the in-house editor immediately.

7.6. Overall Recommendation

Please provide an overall recommendation for the next processing stage of the manuscript as follows:

• Accept in Present Form: The paper can be accepted without any further changes.
• Accept after Minor Revisions: The paper can in principle be accepted after revision based on the reviewer’s comments. Authors are given five days for minor revisions.
• Reconsider after Major Revisions: The acceptance of the manuscript would depend on the revisions. The author needs to provide a point-by-point response or provide a rebuttal if some of the reviewer’s comments cannot be revised. Usually, only one round of major revisions is allowed. Authors will be asked to resubmit the revised paper within ten days and the revised version will be returned to the reviewer for further comments.
• Reject: The article has serious flaws, makes no original contribution, and the paper may be rejected with no offer of resubmission to the journal.

Note that your recommendation is visible only to journal editors, not to the authors. Decisions on revisions, acceptance, or rejections must always be well justified.

7.7. Guidelines for Reviewers for Registered Reports Papers

The review process for Registered Reports is divided into two stages. In Stage 1, reviewers assess study proposals before data is collected. In Stage 2, reviewers consider the full study, including results and interpretation.

When reviewing Stage 1 papers, note that no experimental data or results will be included. Reviewers only need to assess the method, including, for example:

1. The importance and soundness of the proposed hypotheses;
2. The suitability and feasibility of the experimental and analysis methodology;
3. Whether there are sufficient details given to replicate the proposed experimental procedures and analysis;
4. Whether there are sufficient outcome-neutral tests of the hypotheses, including positive controls and quality checks.

Manuscripts that pass Stage 1 peer review may be published immediately or after the successful completion of Stage 2 (at the authors’ discretion). Editorial decisions will not be based on the importance or novelty of the results.

For Stage 2 manuscripts, reviewers will be asked to appraise:

1. Whether the data was adequate to test the proposed hypotheses by satisfying the approved outcome-neutral conditions (such as quality checks, positive controls);
2. Whether the stated hypotheses tested was the same as the approved Stage 1 submission;
3. Whether the authors adhered precisely to the registered experimental procedures or were able to sufficiently justify any changes;
4. Whether any new analyses (not mentioned at Stage 1) are methodologically sound and relevant;
5. Whether the authors’ conclusions are justified given the data.

7.8. Guidelines for Reviewers for Depositing Review Activities into ORCID

MDPI allows reviewers to deposit their review activities into an ORCID iD if the reviewer’s ORCID account is connected to their MDPI Submission System (SuSy) account. To do this, reviewers should register a SuSy account and connect their ORCID here. Once the accounts are connected, reviewers can deposit their review records manually here. These records should then show on the reviewer’s ORCID profile.