Settling the order of authors
Once a team has settled who qualifies as an author, the order of the names on the byline is a decision of its own: the first and last places are the most coveted, the authors between them are usually listed by how much each contributed, and authors who contributed equally still have to be put in some order.
Deciding the order
Once a research team has settled who qualifies as an author, it must decide in what order to list the authors. This can be hard, partly because ordering conventions vary between fields, guidelines and journals, and the ICMJE guidelines give no guidance on how to determine author order. Some journals offer guidance that can help. With professional guidance from medical writers and editors and some easy strategies, a team can agree on a fair order.
The first, last and corresponding authors
The two most coveted positions are first and last. The first author is most often the person who contributed most to the work, whether by designing the study, performing experiments, collecting or analysing data, writing the manuscript or other tasks related to the project. The last author is usually, though not always, the supervisor or principal investigator who oversaw the project. In some fields, the person who oversaw the project may be listed first instead. That person often receives much of the credit when the project succeeds, and the criticism when something goes wrong.
The corresponding author takes primary responsibility for communicating with the journal: they make sure all the required information is submitted, and they receive every update on the submission, such as its status, the reviewers' comments and the final decision. The corresponding author is often the person who oversaw the project, so most teams designate the last or first author as corresponding author.
Authors between the first and last
Between the first and last positions, authors are usually listed by their relative contribution to the work, from most to least. Many teams determine this order mathematically: they choose which items will appear in the manuscript, determine how much each author contributed to each item, rank the items by their importance to the manuscript, calculate each author's total contribution, and order the authors from most to least.
Authors who contributed equally
A team may believe, or calculate, that more than one author contributed equally, and equal contribution can apply to any position in the order, including the first and last. Some journals let a team indicate that authors contributed equally, but the team still has the sometimes daunting task of choosing the order among them.
The task can be harder still when the equal contribution applies to the coveted first or last position. The first "first" author gets more visibility than the other, because that name is the first, and sometimes only, one a reader sees, and the last "last" author often gets the most credit for the work.
A simple way to order equal contributors is alphabetically, although its use has declined over time. Some teams order them instead by seniority in the group, by the difficulty of carrying out a specific part of the project, or by a combination of these. Other teams get creative: a researcher at Stanford University had two researchers in his laboratory play three games, and the winner was given the first slot, an unconventional approach that added a fun spin to an otherwise daunting task. A team can agree, before any dispute arises, to settle the order the same way, by having two authors play a game.
Gender and the order of equal contributors
An analysis of 2,898 scientific papers published between 1995 and 2017 in which two or more authors shared the first-author position found gender inequalities among the authors who contributed equally. Where the first and second authors contributed equally, mixed-gender pairs were most frequent, followed by male–male and then female–female pairs, and in mixed pairs more men were in the first position, although the disparity decreased over time. Where three or more authors contributed equally, there were more men than women in the first position and more all-male than all-female combinations. These inequalities are not consistent with random or alphabetical ordering of authors. The analysis's authors hold that the results raise concerns about women not receiving proper credit for publications and suggest a need for journals to ask for clarity on how the order among equal contributors was decided.