A scientific journal first appeared in 1665; citation of manuscripts began in 1752 [6, 34]. In 1955, the impact factor (IF) was proposed by Eugene Garfield as a simple method to calculate the relative frequencies of citations between journals (Fig. 1) [21]. Subsequently, the IF was used to select journals for the Science Citation Index (SCI), a commercial property of the Institute of Scientific Information (ISI; Philadelphia, PA, USA) and founded by Garfield in 1961 [21]. (ISI subsequently was acquired by Thomson Scientific & Healthcare in 1992, a company that then subsequently became Thomson Reuters.) Beginning in 1975, the IF was incorporated into the newly developed annual Journal Citation Reports (JCR).