The Impact Factor: The Archives Breaks From the Pack

Abstract

In two previous editorials, we have discussed the impact factor (IF) metric, with a particular focus on sex and gender-related journals (Zucker & Cantor, 2003, 2005). Although the IF has been around for a long time now, not everyone is familiar with it, so we will provide its operational definition for the newly curious. Calculated each year by the Institute for Scientific Information, a journal’s IF for a given year is a measure of the frequency with which its recent articles are cited on average during that year. “Recent” refers to the two prior calendar years. Thus, a journal’s IF for a year is calculated as the total number of times any article from the journal is cited over the two prior years, divided by the total number of articles that the journal published during those 2 years. For example, to calculate the IF for Journal X for 2004, one would count the number of times articles from Journal X were cited in 2002 and 2003 and divide it by the number of articles that Journal X published in 2002 and 2003. Although the IF is the best known metric for citation analysis, there are other measures, including the Immediacy Index (II) and the Cited Half-Life (CHL). The II is a measure of how frequently the journal’s “average article” is cited the same year in which it is published. Thus, the II for a year is calculated as the number of times articles from that journal are cited during that year, divided by the number of articles that journal published that year. The CHL is a measure of the longevity of the frequency of citations to the journal, that is, for how long the average article maintains its currency. The CHL for a year is determined by the number of prior publication years required to account for a cumulative total of 50% of that year’s citations to the journal.