Letters may not include references to submitted papers or unpublished results, requests to cite the Letter writer's work, accusations of misconduct, calls for retraction, or personal comments to an author.Legends should only include brief descriptions of the figures. Letters are limited to 500 words, 2 graphical elements (figures or tables), and 10 references.Letters to the Editor provide brief comments that allow readers to constructively address a difference of opinion with authors of a PNAS article. All Brief Reports follow the Direct Submission mode of review and are not eligible as member-contributed submissions.Supporting information (SI) is limited to extended methods, essential supporting datasets, and videos (no additional tables or figures).Brief Reports are limited to 3 pages, which is approximately 1,600 words (including the manuscript text, title page, abstract, and figure legends), and 15 references.All Brief Reports are published open access.Learn more about the Contributed Submissions process.īrief Reports describe observations of immediate impact that may hold potential to initiate new avenues of research, provide compelling new data on controversies of broad interest and long-standing questions, or present a concise conceptual advance. Contributed Submissions: NAS members may contribute two research manuscripts annually within their area of expertise in which they had a direct, significant role in the design and execution of the work.Direct Submissions: Most PNAS articles are Direct Submissions.A standard 6-page article is approximately 4,000 words, 50 references, and 4 medium-size graphical elements (i.e., figures and tables). The preferred length of these articles is 6 pages, but PNAS allows articles up to a maximum of 12 pages.

Research Reports describe the results of original research of exceptional importance.

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