The Impact Factor: “Goin’ Up”

Abstract

Two years ago, an Editorial discussed the impact factor (IF) metric, with a particular focus on sex and gender-related journals (Zucker & Cantor, 2003). Penin-cheek, it was noted that there was nothing more heartwarming than to hear a colleague call out, after a few drinks in a darkened bar in the middle of a scientific meeting, “What’s the impact factor?” This Editorial provides a summary of IF data for the year 2003. To review, the operational definition of the IF used by the Institute for Scientific Information (ISI) is as follows: 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 articles from the journal are cited over the two prior years, divided by the total number of articles that the journal published during those two years. For example, to calculate the IF for Journal X for 2002, one would count the number of times articles from Journal X were cited in 2000 and 2001 and divide it by the number of articles that Journal X published in 2000 and 2001. 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, i.e., for how long the average article maintains its currency. The CHL for a year is determined by the number of prior publication years