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J Investig Med. 2007 May;55(4):174-80. doi: 10.2310/6650.2007.06044.

The meaning of author order in medical research.

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University of Toronto Radiology Residency Training Program, University of Toronto, Toronto, Canada.



Manuscript authorship and author placement have important implications for accountability and allocation of credit. The objective of this study was to assess the relationship between an author's place in the author list and the type of contribution reported by that author. This pattern was then used to develop a method by which author responsibility and accountability can be clarified.


The published contributions of each author of original research articles with a minimum of four authors published in the Journal of the American Medical Association, the British Medical Journal, The Lancet, and the Canadian Medical Association Journal in a 3-year period after author contribution forms were required were coded into 1 of eleven contribution categories. The contributions were grouped according to first, second, middle, and last author and compared by position.


For most categories of contribution, the levels of participation were highest for first authors, followed by last and then second authors. Middle authors had lower levels particularly in conception, drafts of the manuscript, supervision, and being a guarantor.


Current patterns of author order and contribution suggest a consistent theme. Based on the results, a proposal is put forth by which author accountability is clarified. In this proposal, authors are classified as either "primary," "contributing," or "senior or supervisory," each with specified contributions. More than one author may be classified into each author category.

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