EDITORIAL

IMPACT FACTOR: DOES THE 80/20 RULE APPLY TO CORTEX?

Henry A. Buchtel and Sergio Della Sala

Cortex hosted a Forum on the Impact Factor (IF) in 2001 (Cortex, 2001, 37: 455-456 & 575-610). In a series of 10 essays and an interview with Eugene Garfield (founder of the Institute for Scientific Information [ISI] and developer of the IF methodology), the IF concept was analyzed, criticized and defended, and proposals for change were introduced. In terms of the definition of the impact of scientific articles, we haven't progressed much in the last five years since the Forum. There have, however, been some changes in this journal, and these changes have led to a dramatic improvement in the IF for Cortex from 1.2 in 2001 to 3.6 for 2005. To remind those who are not familiar with the definition of IF, an IF of 3.6 for 2005 means that there were, on average, 3.6 citations in 2005 to each of the 89 articles published in 2003 and 2004. The journal's Cited Half-Life is greater than 10.0 years (which means that articles published more than 10 years ago were cited this year at the same frequency as articles published in the last 10 years), and the Immediacy Index for 2005 is now 1.23 (the immediacy index looks at how many articles published in 2005 were cited by journals published the same year); in 2001, the immediacy index was considerably lower (0.19). Why did these improvements occur and what does they mean for the future of the journal. To answer these questions, we looked at Scopus ® and the ISI Web of Knowledge ®.

One non-trivial explanation for the higher IF is that the quality of the articles being published in Cortex has improved in recent years through a more stringent refereeing process. However does this increment in citation spread over all manuscripts published in Cortex equally? It is well known that there is a skewed distribution of citations in most fields (Garfield, 2006). This has been labeled as the 80/20 rule: 20% of the articles account for 80% of the citations, and is one of the strongest arguments against the use of journal IF to evaluate the quality of individuals' work.

Some articles published in 2003-2004 have been cited very frequently but there are few if any articles that were published in that two year period that did not find their way into the reference list of an article in the next year or two. Looking at the articles in the 2003 and 2004 volumes (which form the basis for the 2005 IF), six of the 42 articles published in 2004 have already been cited more than ten times (range 13-23); 19 of the 47 articles in the 2003 volume have been cited more than ten times (range 12-30). One of the 2004 papers has been cited more than twenty times; seven articles from 2003 already enjoy that distinction. On the other hand several papers were quoted less than average. Six of the 2003 papers have never been cited (one from the 2004 issues), several papers were cited only once or twice (12 from 2003 and 20 from 2004), while three and six articles were quoted three times in 2003 and 2004, respectively. To see if the 80/20 rule applies in the 2005 IF, we examined the citation record of the 18 most highly cited Cortex articles from the 89 citable articles published in 2003 and 2004. The impact factor is based on a total of 319 citations of these articles between the time they were published and the end of 2005. In this period of time, these 18 articles were cited 226 times, which is 70.8% of all citations recorded. This is lower than the expected 80%, but close.

Are there any special characteristics of the high-citation rate articles published in 2003 and 2004? To date, the most cited article from 2003 (30 citations) was "Event-induced theta responses as a window on the dynamics of memory" (Bastiaansen & Hagoort). Close behind (27-28 citations) are articles on "The role of theta-range oscillations in synchronizing and integrating activity in mnemonic networks" (Kirk & Mackar), Engagement of lateral and medial prefrontal areas in the ecphory of sad and happy autobiographical memories" (Markowitsch, Vandekerckhove, Lanfermann & Russ), and "What can we infer from double dissociations?" (Dunn & Kirsner). The six papers published in 2004 that already have more than ten citations include "Neuroimaging of performance monitoring: Error detection and beyond" (Ullsperger & von Cramon), "Impaired working memory for location but not for colour or shape in visual neglect: A comparison of parietal and non-parietal lesions" (Pisella, Berberovic & Mattingley), "Anosognosia for plegia: Specificity, extension, partiality and disunity of bodily unawareness (Marcel, Tegnér, & Nimmo-Smith), "The anatomy of anosognosia for hemiplegia: A meta-analysis (Pia, Neppi-Modona, Ricci & Berti), "Anosognosia: The neurology of beliefs and uncertainties" (Vuilleumier), and "The number space and neglect (Vuillemier, Ortigue & Brugger). The themes of memory or consciousness (awareness/neglect/anosognosia) are represented in the titles of most of these papers, reflecting the centrality of these concepts in neuropsychology. The paper on double dissociations by Dunn & Kirsner covers the topic of memory as well, but as one of the areas for discussion rather than as central issue; the error-detection paper is the only paper unrelated to memory or consciousness, though one could argue that by asking the subjects in this study to monitor their errors, the question of consciousness is relevant.

It's important to know where the articles that refer to Cortex publications are published. Most journal editors are pleased when articles in their journal are cited by readers who publish their papers in other respected journals. Of course there were citations in articles subsequently published in Cortex (N=17), but in addition articles from 48 different journals have made 219 citations of papers published in the 2003 and 2004 volumes of Cortex. ISI Web of Knowledge (c) provides information about the IF of the journals in which Cortex articles were cited. Some, like Science, have very high IFs and this enhances the reputation of Cortex, which can further be expected to grow the Cortex IF. To the authors who have helped improve the journal and to the editorial board and the community of referees, we extend a hearty expression of gratitude.

REFERENCES

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