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Journal Citation Reports - The Impact Factor and Other Metrics: JCR Terminology

A brief introduction to using JCR for locating and interpreting the impact factor for journals. Included is the Eigenfactor metrics and other aggregate impact factors.

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For a complete glossary of JCR terms click here.

Aggregate Cited Half-Life:  For both journals and subject categories, the cited half-life is the median age of the articles that were cited in the JCR year. It indicates  the turnover rate for a body of work on a subject.

Cited Half-Life:  The median age of the articles cited in the JCR year. Half of a journal's cited articles were published more recently than the cited half-life. Only journals cited 100 or more times in the JCR year have a cited half-life.

Eigenfactor Score:  A calculation based on the number of times articles from the journal published in the past five years have been cited in the JCR year.  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.

Article Influence Score:  This statistic 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, 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.  A score greater than 1.00 indicates that each article in the journal has above-average influence, and a  score less than 1.00 indicates that each article in the journal has below-average influence.

Immedicacy Index:  The average number of times an article is cited in the year it is published.   The journal Immediacy Index indicates how quickly articles in a journal are cited.

Journal Impact Factor:  This is the average number of times articles from the journal published in the past two years have been cited in the JCR year. The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years. 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.

5-Year Journal Impact Factor:  this calculation is the average number of times articles from the journal published in the past five years have been cited in the JCR year. It is calculated by dividing the number of citations in the JCR year by the total number of articles published in the five previous years.  The 5-year Impact Factor is available only in JCR 2007 and subsequent years.

Journal Ranking: The Journal Ranking table shows the ranking of the current journal in its subject categories based on the journal Impact Factor.

Journal Self-Citation: A reference to an article from the same journal.

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