Journal Impact Factor
The Impact Factor (IF) of a journal is the average number of times articles from the journal published in the past two years have been cited in the JCR year.
An Impact Factor of 1.0 means that, on average, articles published one or two year ago have been cited one time. An Impact Factor of 2.5 means that, on average, the articles published one or two year ago have been cited two and a half times.
The journal Immediacy Index indicates how quickly articles in a journal are cited. The Immediacy Index is the average number of times an article is cited in the year it is published.
Journal Cited Half-Life
The median age of the articles that were cited in the JCR year. Half of a journal's cited articles were published more recently than the cited half-life. For example, in JCR 2001 the journal Crystal Research and Technology has a cited half-life of 7.0. That means that articles published in Crystal Research and Technology between 1995-2001 (inclusive) account for 50% of all citations to articles from that journal in 2001.
Journal Citing Half-Life
The citing half-life is the median age of articles cited by the journal in the JCR year. For example, in JCR 2003, the journal Food Biotechnology has a citing half-life of 9.0. That means that 50% of all articles cited by articles in Food Biotechnology in 2003 were published between 1995 and 2003 (inclusive).
The Eigenfactor Score calculation is based on the number of times articles from the journal published in the past five years have been cited in the JCR year, but it also considers which journals have contributed these citations so that highly cited journals will influence the network more than lesser cited journals. References from one article in a journal to another article from the same journal are removed, so that Eigenfactor Scores are not influenced by journal self-citation.
Click here for more information about Eigenfactor Scores and Article Influence Scores.
Article Influence Score
The Article Influence determines the average influence of a journal's articles over the first five years after publication. It is calculated by dividing a journal’s Eigenfactor Score by the number of articles in the journal, normalized as a fraction of all articles in all publications. This measure is roughly analogous to the 5-Year Journal Impact Factor in that it is a ratio of a journal’s citation influence to the size of the journal’s article contribution over a period of five years.
The mean Article Influence Score is 1.00. A score greater than 1.00 indicates that each article in the journal has above-average influence. A score less than 1.00 indicates that each article in the journal has below-average influence.
Journal Citation Report (JCR) by Web of Science, a report which is released around June annually, is a tool which can be used to evaluate journals, by looking at the Journal Impact Factor (JIF) of the journals.
This video by Clarivate Analytics explains how the Journal Impact Factor is calculated, and how to use JCR to obtain the JIF of a journal and to compare journals in similar fields/disciplines.