Impact factors were released this week. The impact factor has long been a measure of a journal’s research output, but in recent years there have many attempts to find alternative ways to expand how research is assessed. This excerpt from Diversity, value and limitations of the journal impact factor and alternative metrics in Rheumatology International explores some of the many other measurements available today.
Over the past decades, there have been many attempts to overcome limitations of the popular JIF and to propose new citation metrics bearing more comprehensive information on citable sources and their scientific value. The latter has become especially important in the age of digitisation and availability of numerous online databases widening prospects of scholarly communication and objective assessment of research output.
One of the significant achievements in the field of scientometrics is the proposition of metrics considering weight, or scientific prestige, of citations from different literature sources. One such proxy for evaluating scientific prestige is the Eigenfactor™, which takes into account the quantity and “quality” of citations, and employs the idea that citations from highly cited journals weigh more than those from less-cited ones . It resembles the way of ranking web pages based on “weight” of hyperlinks to a web page and is calculated using an algorithm similar to Google’s PageRank. An important advantage of the Eigenfactor over JIF is that it is not an average estimation of the impact. Notably, the Eigenfactor strongly correlates with JIF  and total citation counts and ranks Nature, Proceedings of the National Academy of Sciences of the United States of America, Science, and the Journal of Biological Chemistryamong top scholarly journals .
Eigenfactor scores are now incorporated in JCR along with Article Influence™ scores. Article Influence scores are derived from Eigenfactor scores divided by citable items of a journal and normalised against the mean Article Influence score of 1.00. Importantly, both new metrics are based on a 5-year time frame and do not take into account journal self-citations .
Other additions to the JCR metrics are the immediacy index and the cited half-life. The immediacy index reflects how often, on average, journal articles are cited in the same year of publication. Apparently, journals with open access and frequent issues, widely visible in prestigious databases and covering rapidly evolving fields of science (e.g. molecular medicine, pharmacology) will have greater values of this metric [37, 38]. The cited half-life defines the number of years (“age”) required to reach 50% of the total citations a journal. It reflects the period for which articles in a journal continue to attract citations . In other words, the cited half-life provides information on how long articles are used by the scientific community and continue impacting science (“ageing”).