Co-First/Equal authorship is when two or more individuals are noted as providing the same or equal contribution(s) to a published work. To find this information in a full text or PDF article, first locate the article in PubMed (or another database), link to the publisher’s site (using the buttons in the upper right corner of a record), download the full text where possible, and check both the “Author Affiliation” and “Footnotes” sections (if one exists) to see if there is any mention of co-first/equal authorship for the research—this is where this information is usually listed.

Here’s an example of co-first authorship on a paper: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0000396. Notice the CO icon next to each of the first authors—hover over this icon to see a complete description.

Here’s an example of equal authorship on a paper: http://science.sciencemag.org/content/sci/early/2007/11/08/science.1151710.full.pdf. Notice the information listed for those author names containing a superscript of 9, 10, 11, or 12—“⁹These authors contributed equally to this work. ¹⁰These authors contributed equally to this work. ¹¹These authors contributed equally to this work. ¹²These authors contributed equally to this work.”

You can learn more about co-first/equal authorship contributions from these articles:

• “Equal” Contributions and Credit: An Emerging Trend in the Characterization of Authorship (2010)  – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2953548/
• Increased co-first authorships in biomedical and clinical publications: a call for recognition (2013) – http://www.fasebj.org/content/early/2013/07/09/fj.13-235630.full.pdf

We would be happy to answer any questions about co-first/equal authorship that you may have, just ask us!