As defined by most journals, shared first authorship means that several first authors have made equal contributions.

In the life sciences, first authors are often not listed alphabetically in spite of having made equal contributions – on the grounds that one person has contributed more than another. A “ranking” of contributions is thus established even in the case of equal contributions. This can give rise to conflict if there is disagreement over the order.

Often the results of several dissertations are combined into one publication because this may lead to a better chance of the article being accepted for publication in a journal with a higher impact factor. This also counteracts the “salami tactics” of small-scale publishing. Doctoral researchers often need first authorships on articles in order to be able to advance to the next stage in their career, however. First-author publications are even a requirement for some doctorates.

In spite of equal authorship, the community and reviewers often only perceive the person who is actually named first (the “main author”) as the first author. Authorship position can also influence scores and citation indices, for example, because first authors in lower positions are not included in the calculation.

If more than three first authors are named, the question arises of how so many people can have contributed an “an equal amount of equal substance” to an article. The editor in charge will often decide whether articles with such lists of authors are acceptable or whether explanatory statements are to be requested.