The average number of authors on scientific articles has increased 5-fold over the last 100 years, from one author per paper in 1913 to more than five authors per paper in 2013 [1], and recent times have seen the rise of hyperauthorship, with one paper listing 5,154 authors [2].

This development has resulted in an increase in authorship-related disputes and misconduct, including ghost, guest, orphan, and forged authorship [3].

Authorship misconduct	Definition
Ghost	Authors who contributed to the work but are not listed, generally to hide a conflict of interest from editors, reviewers, and readers.
Guest	Individuals given authorship credit who have not contributed in any substantive way to the research but are added to the author list by virtue of their stature in the organization.
Orphan	Authors who contributed materially to the work but are omitted from the author list unfairly by the drafting team.
Forged	Unwitting authors who had no part in the work but whose names are appended to the paper without their knowledge to increase the likelihood of publication.

Table modified from [3]

In an effort to curtail such disputes, some higher-ranking journals have developed authorship guidelines (see an example here [4]). However, not all journals provide such guidance and the definition of authorship varies across disciplines, geographically, and even between research groups [3].

In this post…

In this post, we discuss current best practices in relation to authorship, including how to distinguish between authors and non-author contributors, how to categorise—and quantify, if needed—the contribution of each author, and how to order author names.

Step 1: List all authors and non-author contributors

Authors

The most widely accepted definition of an author is from the International Committee of Medical Journal Editors (ICMJE). The ICMJE recommends that authorship be based on the following criteria* [5]:

1. Substantial contributions to the conception OR design of the work; OR the acquisition, analysis, OR interpretation of data for the work; AND
2. Drafting the work OR revising it critically for important intellectual content; AND
3. Final approval of the version to be published; AND
4. Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

*Use of this definition can vary across journals. For example, PLOS Medicine requests that all four ICMJE criteria are met by all authors; however, in other PLOS journals, authors need only have met the first, third and fourth criteria [6]. Therefore, we suggest you consult your target journal’s requirements before submission.

Non-author contributors

A non-author contributor is any collaborator who fails to meet all four criteria listed above but who provided financial, conceptual, instrumental-technical, moral, or editorial† assistance [5,7]. Non-author contributors should be acknowledged, and their contributions specified.

Editorial assistance

There is no consensus on whether the assistance of professional editing companies should be acknowledged. Acknowledgment is encouraged [5]; however, it appears most authors forego this recommendation [7]. A recent survey indicated that both authors and editors may wish to avoid acknowledging editorial support, for different reasons [7]. Authors appear to think acquiring professional editorial support reflects badly on them in the eyes of evaluators and funders. Editors, on the other hand, have concerns about changes made to the article after their input has ended, and they feel that an acknowledgement may constitute an endorsement of the study’s conclusions [7]. However, with momentum gaining ground for greater transparency in scholarly communication, some journals, e.g., JAMA, have made it mandatory to acknowledge any persons who provided writing or editing assistance [12].

Below are some real examples of non-author contributions listed in the acknowledgments:

Non-author contributions	Ref.
The authors thank Dr V.L. Hunt for her helpful advice on Metarhizium culture and preparation of conidial suspensions, and Dr R.A. Humber at ARSEF, ARS Biological Integrated Pest Management Research Unit, United States Department of Agriculture, for provision of M. acridum.	[8]
The authors wish to acknowledge the input and valuable help in discussion of the subject from Drs. Naveed Sattar, and John McMurray, BHF Cardiovascular Research Centre University of Glasgow, Glasgow, United Kingdom.	[9]
The authors thank Dr. Jan-Thorben Sieweke for his help in preparing the figures.	[10]
We would like to thank Ms. Margaux McBirney, Ms. Michelle Pappalardo, Ms. Hannah Kimbel and Mr. Ryan Thompson for technical assistance, Dr. Millissia Ben Maamar and Dr. Kevin Arnold for critically reviewing the manuscript. We also acknowledge Ms. Amanda Quilty for assistance in editing the manuscript and Ms. Heather Johnson for assistance in preparation of the manuscript.	[11]

Step 2: Categorise—and quantify, if needed—the contribution of each author

Recently, a standardised taxonomy of the roles and contributions in scholarly publications was developed (Contributor Roles Taxonomy [CRediT]; https://www.casrai.org/credit.html [13]), which consists of 14 taxa.

#	Role	Definition
1	​Conceptualization	​Ideas; formulation or evolution of overarching research goals and aims.
2	Data curation	Management activities to annotate (produce metadata), scrub data and maintain research data (including software code, where it is necessary for interpreting the data itself) for initial use and later re-use.
3	Formal analysis	Application of statistical, mathematical, computational, or other formal techniques to analyse or synthesize study data.
4	Funding acquisition ​	​Acquisition of the financial support for the project leading to this publication.
5	​Investigation	​Conducting a research and investigation process, specifically performing the experiments, or data/evidence collection.
6	​Methodology	​Development or design of methodology; creation of models.
7	Project administration ​	​Management and coordination responsibility for the research activity planning and execution.
8	​Resources	​Provision of study materials, reagents, materials, patients, laboratory samples, animals, instrumentation, computing resources, or other analysis tools.
9	​Software	​Programming, software development; designing computer programs; implementation of the computer code and supporting algorithms; testing of existing code components.
10	​Supervision	​Oversight and leadership responsibility for the research activity planning and execution, including mentorship external to the core team.
11	​Validation	​Verification, whether as a part of the activity or separate, of the overall replication/reproducibility of results/experiments and other research outputs.
12	​Visualization	​Preparation, creation and/or presentation of the published work, specifically visualization/data presentation.
13	Writing – original draft ​	​Preparation, creation and/or presentation of the published work, specifically writing the initial draft (including substantive translation).
14	Writing – review & editing ​	Preparation, creation and/or presentation of the published work by those from the original research group, specifically critical review, commentary or revision – including pre- or post-publication stages.

Table copied from [13].

Below are some real examples of this taxonomy in use (1) as it was intended and (2) modified by the authors to include more detail:

#	Contributions	Ref.
1	Conceptualization, W.A.H., A.T. and P.K.; Methodology, W.A.H., A.T. and P.K.; Software, W.A.H. and A.T.; Investigation, W.A.H. and A.T.; Data Curation, W.A.H. and A.T.; Writing – Original Draft, W.A.H. and P.K.; Writing – Reviewing and Editing, W.A.H., A.T. and P.K.; Visualization, W.A.H.; Funding Acquisition, P.K.	[14]
2	Conceptualization, A.A.H., D.S.G. and R.T.; Methodology and Investigation: Performed the parasite functional analysis, R.J.W., A.F., D.B., M.P., D.S.G., and R.T; DNA content analysis; R.J.W., B.F.F., C.J.J., D.S.G., and R.T.; Performed IFA and Cell Biology, R.J.W., A.F., S.W., and R.T.; Immunoprecipitation experiments, R.J.W., M.Z., A.R.B., and R.T.; qRT-PCR analysis, R.J.W. and A.F.; Yeast two-hybrid experiments, H.Y.; Electron microscopy experiments, D.J.P.F.; Resources, D.J.P.F., C.J.J., H.Y., and R.T.; Writing – Original Draft, R.J.W., D.S.G., and R.T.; Writing – Review & Editing, R.J.W., A.M.F., C.J.J., A.A.H., D.S.G., R.T., and all others contributed; Project Administration, D.B. and R.T.; Supervision, A.A.H. and R.T.	[15]

How to quantify an author’s contribution?

With the rising incidence of authorship disputes and misconduct, and rising interest from the scientific community to improve authorship transparency [16], many metrics have been developed to quantify—rather than simply qualify—the contribution of each co-author [17,18]; however, none have been widely recognised or adopted by scientific journals.

The adoption of the recently developed Author Contribution Index (ACI) by the journal Rethinking Ecology may represent a turning point in authorship transparency reform [19]. The ACI is a simple (and universal) metric based on a single percentage contribution for each co-author [16].

Below is a real example from a recent Rethinking Ecology article [20]:

Briefly, an ACI = 9.286 means that this author contributed 9.286 times more than what the other authors contributed on average. See [16] for the ACI formula.

It is unlikely you will be required to quantify author contribution any time soon. However, if the ACI proves successful, it could be adopted by other journals. And it would be wise to begin implementing the practice of openly discussing contribution—in terms of percentages—with collaborators, even if not specifically requested by journals.

Step 3: Determine the order in which author names should be presented

There are no standardised guidelines for the sequence author names should follow in scientific articles. Authorship policies range from alphabetical to descending order of contribution, with policies varying across disciplines [21]. As such, authorship order has generally no agreed upon meaning.

You should consult the target journal, and/or your institution’s, guidelines for specific advice regarding authorship ordering. Disputes over an authorship sequence can usually be overcome by providing an author contribution—qualitative and quantitative—statement (see steps 1 and 2).

Conclusion

Journal policies regarding authorship are in a state of flux. The number of articles focusing on the issue of co-authorship has seen a sharp increase in recent years [19]. As the momentum for greater transparency increases, you should consider investing time in implementing the latest best practices.

References

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2. ATLAS, CMS collaboration. Combined measurement of the Higgs Boson mass in pp collisions at s√=7 and 8 TeV with the ATLAS and CMS experiments, Phys Rev Lett. 2015 May 14;114(19):191803.
3. McNutt MK, Bradford M, Drazen JM, Hanson B, Howard B, Jamieson KH, Kiermer V, Marcus E, Pope BK, Schekman R, Swaminathan S. Transparency in authors’ contributions and responsibilities to promote integrity in scientific publication. Proc Natl Acad Sci. 2018 Mar 13;115(11):2557-60.
4. Nature. Authorship. Available from: https://www.nature.com/authors/policies/authorship.html [Accessed 30 April 2019].
5. ICMJE. Defining the role of authors and contributors. Available from: http://www.icmje.org/recommendations/browse/roles-and-responsibilities/defining-the-role-of-authors-and-contributors.html [Accessed 30 April 2019].
6. Kiermer V, Peiperl L. PLOS collaborates on recommendations to improve transparency for author contributions. PLOS Blogs. 2019 Feb 27. Available from: https://blogs.plos.org/plos/2018/02/guidelines-transparency-for-author-contributions/ [Accessed 30 April 2019].
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8. Clancy LM, Jones R, Cooper AL, Griffith GW, Santer RD. Dose-dependent behavioural fever responses in desert locusts challenged with the entomopathogenic fungus Metarhizium acridum. Sci Rep. 2018 Sep 21;8(1):14222.
9. Kristensen SL. Individualizing surgical revascularization in patients with ischaemic heart failure—a further dive into STICHES. Eur J Heart Fail. 2019 Mar 1;21(3):382-4.
10. Riehle C, Bauersachs J. Of mice and men: models and mechanisms of diabetic cardiomyopathy. Basic Res Cardiol. 2019 Jan 1;114(1):2.
11. Kubsad D, Nilsson EE, King SE, Sadler-Riggleman I, Beck D, Skinner MK. Assessment of glyphosate induced epigenetic transgenerational inheritance of pathologies and sperm epimutations: generational toxicology. Sci Rep. 2019 Apr 23;9(1):6372.
12. JAMA. Instructions for authors. Available from: https://jamanetwork.com/journals/jama/pages/instructions-for-authors#SecAcknowledgmentSection [Accessed 30 April 2019].
13. Casrai. CRediT. Available from: https://www.casrai.org/credit.html [Accessed 30 April 2019]
14. Haynes WA, Tomczak A, Khatri P. Gene annotation bias impedes biomedical research. Sci Rep. 2018 Jan 22;8(1):1362.
15. Wall RJ, Ferguson DJ, Freville A, Franke-Fayard B, Brady D, Zeeshan M, Bottrill AR, Wheatley S, Fry AM, Janse CJ, Yamano H. Plasmodium APC3 mediates chromosome condensation and cytokinesis during atypical mitosis in male gametogenesis. Sci Rep. 2018 Apr 4;8(1):5610.
16. Boyer S, Ikeda T, Lefort MC, Malumbres-Olarte J, Schmidt JM. Percentage-based Author Contribution Index: a universal measure of author contribution to scientific articles. Res Integr Peer Rev. 2017 Dec;2(1):18.
17. Verhagen JV, Wallace KJ, Collins SC, Scott TR. QUAD system offers fair shares to all authors. Nature. 2003 Dec 11;426(6967):602.
18. Warrender JM. A simple framework for evaluating authorial contributions for scientific publications. Sci Eng Ethics. 2016 Oct 1;22(5):1419-30.
19. Boyer S, Lefort M-C, Winder L. Rethinking ecology—challenging current thinking in ecological research. Rethink Ecol. 2016 Nov 22;1:1–8.
20. Morley CG, Broadley J, Hartley R, Herries D, MacMorran D, McLean IG. The potential of using Unmanned Aerial Vehicles (UAVs) for precision pest control of possums (Trichosurus vulpecula). Rethinking Ecol. 2017 Oct 23;2:27.
21. Brand A, Allen L, Altman M, Hlava M, Scott J. Beyond authorship: attribution, contribution, collaboration, and credit. Learn Publ. 2015 Apr;28(2):151-5.