Two researchers do roughly equal amounts of the central work on a paper, but only one name can physically come first on the author line. This is now an everyday situation in team science, and the conventional response is to declare the two authors equal contributors. Yet that declaration is recorded in many different ways, some of which barely survive indexing, and the result is that genuinely shared credit is frequently lost when it matters most — in a hiring or promotion committee reading the line. This article sets out how to mark shared credit correctly, building on the conventions described at author order and the role definitions at the CRediT roles.
What “equal contribution” is claiming
In most experimental and biomedical fields, position on the author line is information, not decoration. By widespread convention the first author did the bulk of the hands-on work and led the writing; the last author is the senior supervising figure. A co-first or equal-contribution designation is a deliberate intervention against that convention: it asserts that two (occasionally more) people share the leading-author role even though the linear author line can only print them one after another. The claim is specifically about leadership of the work, and it should be reserved for cases where it is genuinely true — not used as a courtesy to soften the awkwardness of ordering.
It is worth being clear that equal contribution is field-specific. In mathematics, economics, and much of the humanities, authors are listed alphabetically and order carries no contribution signal at all, so an equal-contribution note is redundant. The designation does real work only where order is otherwise read as a ranking.
The three places shared credit gets recorded
Shared first authorship can be expressed through three distinct mechanisms, and the strongest practice uses them together rather than relying on any one.
1. The author-line note
The familiar device is a symbol against two or more names — commonly a superscript dagger or asterisk — resolving to a footnote that reads “These authors contributed equally to this work.” This is the human-readable signal a reader sees on the page. Its weakness is that it is presentational: the symbol and its note are not reliably captured as structured metadata, so a system harvesting the author list may record the two authors in their printed order and silently drop the equality. That is precisely how co-first status disappears downstream.
2. The contribution statement, using the degree qualifier
This is where a contribution taxonomy earns its place. The CRediT taxonomy supports an optional degree-of-contribution qualifier on every role assignment: lead, equal, or supporting. It is not a percentage and it does not weigh one role against another; it simply distinguishes who led a role from who shared or supported it. To record co-first authorship honestly, mark the relevant leading roles — typically Conceptualization, Investigation, Formal analysis, and Writing – original draft — as equal for both authors:
Author A: Conceptualization (equal), Investigation (equal), Writing – original draft (equal). Author B: Conceptualization (equal), Investigation (equal), Writing – original draft (equal).
This carries far more information than a footnote. It says which parts of the work were shared, and it does so in a form that can travel into structured systems. The qualifier is widely available in publisher submission systems, though rarely required, so you usually have to choose to use it.
3. Order-neutral display where the venue allows
A growing number of venues let authors indicate that the printed order of co-first authors may be swapped on individual CVs — the “authors may list their name first” convention. Where offered, this is a sensible complement to the two mechanisms above, because it acknowledges directly that the linear order does not encode a ranking between the equal contributors.
A method for marking it correctly
- Confirm the claim is true. Equal contribution means the leading work was genuinely shared. If one person clearly led, say so with lead and supporting rather than reaching for equal.
- Decide the printed order on a transparent basis. Something has to come first. Agree the basis openly — alphabetical, coin-toss, or rotation across the group’s papers — and record that the order is not a ranking.
- Add the author-line note so a human reader sees the equality at a glance.
- Encode it in the CRediT statement with the equal qualifier on the shared roles, so the claim survives as structured data rather than as a presentational footnote.
- Have every named author confirm their own line before submission. Shared-credit claims are exactly where unconfirmed assumptions cause later disputes.
Common mistakes
- Relying on the footnote alone. A dagger and a note are fragile. Without the structured qualifier, the equality often does not survive into the systems that later read the author list.
- Using “equal” to avoid an honest conversation. Declaring everyone equal because ordering is uncomfortable devalues the designation and misrepresents the work.
- Confusing equal contribution with author order generally. CRediT records what each person did; it does not set author order, which remains a separate decision governed by your field’s conventions.
- Forgetting the corresponding-author role. Corresponding authorship is a distinct responsibility and can sit with any author, including one of the co-first authors; settle it explicitly.
Where shared vocabulary fits
“Co-first”, “joint first”, “equal contribution”, and “shared senior author” are used loosely and recorded inconsistently across venues, which is exactly why the credit so often fails to travel. A shared, federated vocabulary that defines these designations precisely — and points back to NISO for the CRediT standard and its degree qualifier — is what lets an equal-contribution claim mean the same thing wherever it is read. Supplying that definitional layer is the role the CASRAI dictionary is designed to play; the relevant terms sit in the CRediT extensions domain.