When impact factors rise, editors editorialize. When they fall, editors fall silent. The impact factor of Stroke has risen from 5.53 in 1999 to 6.008 in 2000. It is time to editorialize. These statistics reaffirm Stroke as the leading publication in the field, place it among the top 3 clinical neurological journals along with Brain and the Annals of Neurology, and make it the leading subspeciality journal in neurology and one of the top publications in peripheral vascular disease. This impact factor was achieved under the editorship of Dr Mark L. Dyken. We congratulate him, his editorial team, the reviewers, and the authors who chose to submit to Stroke and who contributed to such a milestone. While we appreciate our newly gained status, we also understand that there are other measures of quality and other considerations, particularly the main purpose of our journal to publish: “Reports of clinical and basic investigation of any aspect of the cerebral circulation and its diseases” (from Stroke Instructions to Authors).
The idea of an impact factor goes back to the 1950s and its use to the early 1960s.1 The numerator consists of “the number of citations in the current year, to any items published in the previous two years” and the denominator consists of “the number of substantive articles (source items) published in the same two years.”1 This definition is like an overcoat, ample but unrevealing, since “substantive articles” can and are defined in various ways by the compilers of the impact factor.
The impact factor is influenced by several variables. The critical determinants of impact are the mean number of citations per article (density) and the half-life of the citations (number of years back from the current year, which cover 50% of all citations).2 However, only a large field with numerous researchers and publications can yield super-cited papers. Papers introducing a new technique, a new model, a new test, diagnostic or outcome criteria, reviews and controversies, also garner their share of citations, and these vary among areas and with different stages of development of a discipline. Impact factor rankings within a field are more meaningful than between fields, since the activity depends on the number of individuals publishing in it. In medicine, Basic Science authors are more numerous and tend to publish more than clinicians, hence basic science journals generally have higher impact factors than clinical journals; thus, impact factors have some value as relative measures in closely related defined categories but do not have validity as absolute or relative measures across categories. A fully mature field replete with investigators may proffer many more papers compared with an incipient but potentially important area, in which the number of publications is sparse and hence the impact factor is low. In reality, however, it is the new discipline that may have the ultimate greater impact on human health and the progress of science.
Despite these limitations, impact factors have become an important, albeit misunderstood, measure of quality. Some universities will take the number of publications, multiply by the impact factor of the journal in which they are published, and arrive at an arbitrary criterion that is used towards promotion. The impact factor is also used and misused in competition. Competition for authors, who may look at a journal’s impact factor as one of the determinants of submission of their manuscripts; competition among journals for prestige and influence; and competition with the larger purpose of a journal. For example, short reports, which may be desirable in that more information is conveyed and attention brought to something that may need and deserve further development, may be less likely to be cited, resulting in diminution of the impact factor3 and thus reducing the journal’s competitiveness among authors. Competing interests may also arise within the same journal. Stroke is read by many neurologists in practice, who are not doing research or publishing. What they are interested in reading—the impact on them—may not be what the authors are interested in publishing. The competition between readers and authors has to be balanced in a journal that aims not only to advance the field of stroke, but also to help practitioners deliver state-of-the-art care and education.
The purpose of Stroke is to publish the best work in our field and to encourage the development of promising areas. This may mean that papers from a new discipline will not achieve a high citation index, and we have to choose between the impact factor, by which we are judged in the short term, and acceptance of a paper that may have an effect on the field in the long term.
In the future, there may be more sophisticated ways of assessing the quality of articles and journals. For example, a Research Index is a software program that can build digital libraries of published scientific papers and produce automatic citation analyses of all the papers cited. It can also compile statistics on user behaviour, thus complementing and perhaps superseding the data available on impact factors.4
While we will remain watchful of our impact factor, and mindful of the competition, we will abide by our main purpose: to publish valid, new, and important papers that advance the field of stroke.