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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.
Only journals cited 100 or more times in the JCR year have a cited half-life.
A higher or lower cited half-life does not imply any particular value for a journal. For instance, a primary research journal might have a longer cited half-life than a journal that provides rapid communication of current information. Cited half-life figures may be useful to assist in collection management and archiving decisions. Dramatic changes in cited half-life over time may indicate a change in a journals format. Studying the half-life data of the journals in a comparative study may indicate differences in format and publication history.
The aggregate cited half-life is calculated the same way as the journal cited half-life, and its significance is comparable. For both journals and subject categories, the cited half-life is the median age of the articles that were cited in the JCR year. The aggregate cited half-life is an indication of the turnover rate of the body of work on a subject.
For example, in JCR 2003 the subject category Energy & Fuels has a cited half-life of 7.0. That means that articles published in Energy & Fuels journals between 1997-2003 (inclusive) account for 50% of all citations to articles from those journals in 2003.
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