Frank's editorial in the January 2003 Journal of the Medical Library Association [1] justifies a critical view of what ISI's impact factor can and cannot tell librarians. I would add that the factor may not properly represent the “impact” of a journal within its own field. Citations of papers in a “small” field are probably largely in just its journals. Hence, their numerators in the impact factor are likely to be smaller than those for broad-field journals. Yes, one can gauge the relative “strengths” of journals in a narrow field by comparing their impact factors, but those factors will be almost certainly smaller than those of broad-scope journals. I have suggested elsewhere [2] that this weakness of impact factors in judgments on journals in narrow-topic fields might be avoided by calculating a version of the factor that takes into account a journal's scope. The calculation divides a journal's impact factor by the number of journals citing its papers; the resulting figure is multiplied by 1,000 to bring the result up to a magnitude similar to (although not identical with) unadjusted impact factors. I have termed this new factor, “the scope-adjusted impact factor” (SAIF). When I calculated it for a leading cardiology and a leading oncology journal, their SAIF factors moved up to about the SAIF for the New England Journal of Medicine, a high-impact-factor journal with a broad scope. I carried out this study in 1990 with data for twenty-five journals; perhaps others might be interested in testing this approach with more recent data.
References
- Frank M. Impact factors: arbiter of excellence? J Med Libr Assoc. 2003 Jan; 91(1):4–6. [PMC free article] [PubMed] [Google Scholar]
- Huth EJ. Mapping the land of medical journals: some new applications for citation data from Science Citation Index. In: Lock S, ed. The future of medical journals: in commemoration of 150 years of the British Medical Journal. London, U.K.: British Medical Journal Books, 1991:81–92. [Google Scholar]