A deficiency in the algorithm for calculating the impact factor of scholarly journals: the Journal Impact Factor.

The Journal Citation Reports ® (JCR), published by the Institute for Scientific Information, annually ranks more than 6,500 science and social science journals, by calculating their impact factors (and many other useful measures) from the citations they receive from journals monitored by ISI in the Science Citation Index (SCI), Social Science Citation Index (SSCI), and Arts & Humanities Citation Index (A&HCI) databases that process about 25 million citations annually. As Eugene Garfield, the founder of ISI, the inventor of the journal impact factor, and the deservedly most cited information scientist defines it: “[t]he annual JCR impact factor is a ratio between citations and recent citable items published. Thus, the impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years, by calculating the ratio between the number of citations received and the number of citable articles published” (Garfield, 1994 [emphases added]). For example, the impact factor of Cortex was determined by the algorithm shown in Figure 1 in the 1999 edition of JCR (the most current as of this writing).