The basic format for reference to an article in an online journal is as follows:
Author(s). Title. Journal Name [using National Library of Medicine abbreviations—see 14.10, Abbreviations, Names of Journals]. Year;vol(issue No.):inclusive pages. URL [provide the URL in this field; no need to use “URL:” preceding it]. Published [date]. Updated [date]. Accessed [date].
Note: Use the URL that will take the reader most directly to the article, not a long search string and not a short, more general URL (one to the publisher’s home page, for example); if a URL is provided, as close as possible to publication verify that the link still works. Patrias11 notes that NLM recommends using the location displayed in the Web browser as the URL. For a journal article, the accessed date will often be the only date available. This is especially important for journals that provide no “versioning” (eg, date posted, date updated or revised).
1. Duchin JS. Can preparedness for biological terrorism save us from pertussis? Arch Pediatr Adolesc Med. 2004;158(2):106-107. http://archpedi.ama-assn.org/cgi/content/full/158/2/106. Accessed June 1, 2004.
Many journals, such as Archives of Pediatrics & Adolescent Medicine in the example above, have parallel print and online publication, and the page numbers of the print article are included in the online citation. In this example, the date the article was posted (ie, published) was not provided and there were no updates, so only the date the article was accessed is listed. The inclusion of the URL and the date accessed, which differentiates this from the citation of the identical article in print, indicates that the online version of the article was seen and hence is appropriately cited.
In the example below, however, the article is only available online and has no page numbers.
2. Gore D, Haji SA, Balashanmugam A, et al. Light and electron microscopy of macular corneal dystrophy: a case study. Digit J Ophthalmol. 2004;10. http://www.djo.harvard.edu/site.php?url=/physicians/oa/671. Accessed December 6, 2005.
Other online-only articles without page numbers may be noted by other identifiers, eg, by e-page numbers (examples 3 and 4) or by article number (example 5).
3. Laupland KB, Davies HD, Low DE, Schwartz B, Green K; Ontario Group A Streptococcal Study Group. Invasive group A streptococcal disease in children and association with varicella-zoster virus infection. Pediatrics. 2000;105(5):e60. http://pediatrics.aappublications.org/cgi/content/full/105/5/e60. Accessed April 30, 2004.
4. e-Health Ethics Initiative. e-Health Code of Ethics. J Med Internet Res. 2000; 2(2):e9. http://www.jmir.org/2000/2/e9. Published May 24, 2000. Accessed April 29, 2004.
Examples 5 and 6 provide the DOI rather than a URL. In this case, it is not necessary to also provide the URL. When the DOI is provided, it is preferable to cite it rather than the URL. Note: The DOI is provided immediately after “doi:” and is set closed up to it, per convention. No accessed date is required for the DOI, making it the last item in the reference.
5. Smeeth L, Iliffe S. Community screening for visual impairment in the elderly. Cochrane Database Syst Rev. 2002;(2):CD001054. doi:10.1002/14651858.CD1001054
6. Kitajima TS, Kawashima SA, Watanabe Y. The conserved kinetochore protein shugoshin protects centromeric cohesion during meiosis. Nature. 2004;427(6974):510-517. doi:10.1038/nature02312
In some cases, different versions of the same article are published in print and online. The BMJ’s ELPS (electronic long, print short) is one example.18 The print journal article (short version) is also made available online. Note: The version consulted is the version that should be cited. If the author consulted the article in the print journal, the reference would be cited like any other print journal article (see 3.11, References to Print Journals).
7. Deeks JJ, Smith LA, Bradley MD. Efficacy, tolerability, and upper gastrointestinal safety of celecoxib for treatment of osteoarthritis and rheumatoid arthritis: systematic review of randomised controlled trials. BMJ. 2002;325(7365):619-623.
If the author consulted the same article online, the reference would be formatted as follows:
8. Deeks JJ, Smith LA, Bradley MD. Efficacy, tolerability, and upper gastrointestinal safety of celecoxib for treatment of osteoarthritis and rheumatoid arthritis: systematic review of randomised controlled trials [abridged]. BMJ. 2002;325(7365):619-623. http://bmj.bmjjournals.com/cgi/content/abridged/325/7365/619. Published September 21, 2002. Accessed October 21, 2002.
If the author consulted the long version of this article, available only online, the reference would be formatted as follows:
9. Deeks JJ, Smith LA, Bradley MD. Efficacy, tolerability, and upper gastrointestinal safety of celecoxib for treatment of osteoarthritis and rheumatoid arthritis: systematic review of randomised controlled trials. BMJ. 2002;325(7365):619. http://bmj.bmjjournals.com/cgi/content/full/325/7365/619. Published September 21, 2002. Accessed October 11, 2002.
Note that the online citation of the long version (example 9) differs from that of the short version (example 8) in that it does not provide inclusive page numbers but gives only the first page in the print journal. Many online journals, however, do use inclusive page numbers.
In the example below, the online article includes a video. This is mentioned in an editor’s note in the print journal; in the online journal, a link to the video appears in the table of contents and as a link within the article. The citation to the print article appears as follows:
10. Bertocci GE, Pierce MC, Deemer E, Aguel F. Computer simulation of stair falls to investigate scenarios in child abuse. Arch Pediatr Adolesc Med. 2001;155(9):1008-1014.
The citation to the online article, containing the video, would be as follows:
11. Bertocci GE, Pierce MC, Deemer E, Aguel F. Computer simulation of stair falls to investigate scenarios in child abuse. Arch Pediatr Adolesc Med. 2001;155(9):1008-1014. http://archpedi.ama-assn.org/cgi/content/full/155/9/1008. Accessed February 27, 2004.
A citation to only the video in the online version would be as follows:
12. Bertocci GE, Pierce MC, Deemer E, Aguel F. Computer simulation of stair falls to investigate scenarios in child abuse [video]. Arch Pediatr Adolesc Med. 2001;155(9):1008-1014. http://archpedi.ama-assn.org/cgi/content/full/155/9/1008/DCI. Accessed February 27, 2004.
In the following example, the online article contains 3 tables not included in the print version. These are cited in the print article as eTable 1, eTable 2, and eTable 3; in the online journal, these appear as links within the article; and on the PDF they appear as pages e1 to e7.
13. DeWitt DE, Hirsch IB. Outpatient insulin therapy in type 1 and type 2 diabetes mellitus: scientific review. JAMA. 2003;289(17):2254-2264, e1-e7. http://jama.ama-assn.org/cgi/content/full/289/17/2254. Accessed December 6, 2005.
If an article is published online ahead of print publication, it may appear in 1 of 3 ways: (1) posted without editing; (2) edited and posted as it will appear in print, only ahead of the print publication (with or without print pagination); or (3) edited and posted as part of a specific issue of the journal. The first is found more often in the physical sciences (eg, physics preprint servers) than in medicine. Examples of the second (example 14) and third (example 15) are given below:
14. van der Hoek L, Pyrc K, Jebbink MF, et al. Identification of a new human coronavirus [published online March 21, 2004]. Nat Med. doi:10.1038.nm1024
In example 14, the article has not yet been paginated in the print journal and the DOI serves as the unique identifier for the article until publication. Once the article has been published in print, the full citation is provided to facilitate linking (see example 15).
15. van der Hoek L, Pyrc K, Jebbink MF, et al. Identification of a new human coronavirus [published online March 21, 2004]. Nat Med. 2004;10(4):368-373. doi:10.1038.nm1024
Example 16 is for an article not yet published in print and example 17 is for the reference once it has been published in print. Note: The title, byline, or other components may have changed slightly between online-only and print publication.
16. Cannon CP, Braunwald E, McCabe CH, et al; Pravastatin or Atorvastatin Evaluation and Infection Therapy—Thrombolysis in Myocardial Infarction 22 Investigators. Comparison of intensive and moderate lipid lowering with statins after acute coronary syndromes [published online March 8, 2004]. N Engl J Med. doi:10.1056/NEJMoa040583
17. Cannon CP, Braunwald E, McCabe CH, et al; Pravastatin or Atorvastatin Evaluation and Infection Therapy—Thrombolysis in Myocardial Infarction 22 Investigators. Intensive vs moderate lipid lowering with statins after acute coronary syndromes [published online March 8, 2004]. N Engl J Med. 2004;350(15):1495-1504. doi:10.1056/NEJMoa040583
Some journals allow the reader to submit an immediate online response to articles (eg, BMJ’s Rapid Responses and Pediatrics' Post-publication Peer Reviews [P3R]). Examples of these are below:
18. Deutsch J. Less is better [Rapid Response]. BMJ. http://bmj.bmjjournals.com/cgi/eletters/328/7438/0-g#51798. Published February 27, 2004. Accessed April 30, 2004.
19. Molloy EJ, Nigro K, Sandhaus L, Watson RWG, Walsh MC. Labor and stress at delivery are confounders in the evaluation of neonatal sepsis [Post-publication Peer Review]. Pediatrics. 2004;113(5):1173. http://pediatrics.aappublications.org/cgi/eletters/113/1173. Published May 28, 2004. Accessed June 2, 2004.