HOW SCIENTIFIC JOURNALS WORK/SPECIAL CONTRIBUTION The Altmetric Score: A New Measure for Article-Level Dissemination and Impact N. Seth Trueger, MD, MPH*; Brent Thoma, MD, MA; Cindy H. Hsu, MD, PhD; Daniel Sullivan, MDiv; Lindsay Peters, BA; Michelle Lin, MD *Corresponding Author. E-mail: ntrueger@gmail.com, Twitter: @MDaware. 0196-0644/$-see front matter Copyright © 2015 by the American College of Emergency Physicians. http://dx.doi.org/10.1016/j.annemergmed.2015.04.022 HISTORICAL PERSPECTIVE The explosion of scientific literature in recent years 1 makes it increasingly important and difficult for clinicians to identify high-quality articles relevant to their practice, research, education, and advocacy efforts. Theoretically, prestigious journals are read widely because of the high impact of their articles on medical practice; journal prestige has traditionally been quantified with the journal impact factor. Initially described by Garfield 2,3 and now published annually by Thomson Reuters, 4 journal impact factor uses citations in other scientific journals to quantify the influence of an original research journal as a whole, calculating the ratio of citations of previous 2 years’ articles during the current year to the total number of citable articles published in that journal during those previous 2 years (Figure 1A and B). 4 Journal impact factor posits that the impact of a journal is the weighted sum of the citations, and therefore the impact, of its articles. Authors’ work has increasingly been assessed by the impact of the journal it is published in for the purposes of university promotions, general esteem among colleagues, 5 and hiring and funding decisions. 6,7 Despite its popularity, journal impact factor is widely criticized. 8 Detractors note that it is inherently slow (citations take months to years to accrue, and journal impact factor is published annually according to 1- to 3-year-old data 9 ), narrow (it assesses only this one particular type of impact 10 during a brief 2-year period 11 ), secretive and irreproducible (articles are weighted according to an opaque and subjective classification such as primary, review, or “front matter,” classifications that are subject to lobbying by publishers 11 ), and open to gaming (some types of articles are cited much more frequently than others 10,11 ), and fails to identify influential articles published in minor journals. Other journal-level metrics have been created but fail to address these issues, 12,13 and the h-index was developed in Volume no. 2005 to measure the impact of authors rather than journals. It combines an individual’s productivity (number of articles) and impact (number of citations) to quantify their contributions. 14 However, it also has drawbacks: it is slow, can be manipulated (eg, self-citation), does not adjust for the number or role of coauthors (particularly because coauthorship has increased significantly 15 ), and poorly recognizes early-career authors or those with small numbers of articles with high impact. 16 ALTMETRICS: ARTICLE-LEVEL METRICS Contrary to citation-based metrics like the journal impact factor and h-index, altmetrics (short for “alternative metrics” or “article-level metrics”) promptly measure the impact of an individual article’s dissemination. 17 The widespread adoption of electronic publishing, paired with the rise of social media for dissemination and discussion of scientific literature, makes it feasible to quantify the discussion of an article on blogs, podcasts, social media platforms, and news media. These measures aim to address many of the failings of traditional impact metrics; they are available nearly instantaneously, measure the dissemination of individual articles, and may more accurately assess total overall readership by incorporating more metrics—primarily measures of social media—rather than simply citations in traditional journals. As a result, highly disseminated articles may be identified within days of their publication. 18-21 Although altmetrics have certain advantages over citation-based metrics such as the journal impact factor and h-index, the type of impact that they measure, although related, is not the same. We propose that altmetrics be thought of as measures of “disseminative impact,” whereas traditional citation-based metrics be considered measures of “scholarly impact.” Altmetrics provide a proxy of a specific article’s overall readership, and articles capable of generating “buzz” are likely to score more highly. 19,20 The journal impact factor and h-index are derived from citations and are likely to link more strongly with the importance of Annals of Emergency Medicine 1

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