A Closer Look at Cited and Citing Half Lives

You’ve seen Cited Half-Life and Citing Half-Life data in Journal Citation Reports (JCR)—there’s a graph and a table of journals listed for every journal in the database with 100 or more citations—but what do they mean? How do you keep them straight between Cited and Citing? Why should you care about them?

First, let’s look at Cited Half-Life. This metric refers to the median age of the citations received by a journal during the JCR year. A citation’s age is equal to the publication year of the citing item (i.e., JCR year) minus the publication year of the cited item. By definition, half of a journal's earned citations are to items published before the Cited Half-Life, and half are to items published after the Cited Half-Life. JCR caps Cited Half-Life at 10 years—any journal scoring over 10 years will display as >10 in the product.

If a journal has a Cited Half-Life of 4, it means the median age of citations is 4 years—half of the citations are to items newer than 4 years, and the other half are older. In the JCR, Cited Half-Life is shown on the Cited Journal Graph as a grey division. So for example, in the journal below, the Cited Half-Life is 9, so half of the citations are to items published after 2007 (9 years back from 2015), and half to items prior to 2007:

CITED-half-life

Cited Half-Life is a good measure if you are interested in looking at a journal and finding out if older or newer material is receiving attention.

Conversely, Citing Half-Life looks at citations given by a journal in the JCR year. It is specifically defined as the median age of the citations produced by a journal during the JCR year. A citation’s age is equal to the publication year of the citing item (i.e., JCR year) minus the publication year of the cited item. By definition, half of a journal's outbound citations are to items published before the Citing Half-Life, and half are to items published after the Citing Half-Life. As with Cited Half-Life, JCR caps Citing Half-Life at 10 years—any journal scoring over 10 years will display as >10 in the product.

If a journal has a Citing Half-Life of 4, it means the median age of citations is 4 years—half of the citations are from items newer than 4 years, and the other half are older. In the JCR, Citing Half-Life is shown on the Citing Journal Graph as a grey division. In the graph below, the Citing Half-Life of the journal is 4.7, so half of the citations are from items published after 2012 (4.7 years back from 2015), and half from items prior to 2012:

CITING-half-life

Citing Half-Life can give you a different perspective on a journal’s relationship to its peers—which journals it cites most, and how far back that citing relationship extends.

According to the JCR’s creator, the late Dr. Eugene Garfield, “One of the major applications of JCR data has been for analyses of journal usage—by librarians faced with decisions about collection maintenance and deacquisition of individual journals, as well as by information scientists and others involved in research concerning entire subject fields of journals.  Chronological data are provided in the Citing and Cited Journal Packages, but not in a form that lends itself to quick identification of usage patterns.  The Journal Half-Life Package presents these data so that chronological patterns are more easily discernible.” Although Dr. Garfield also went on to say that the significance of ranking by Half-Life has not yet been determined, the Half-Life for a journal can help librarians decide how far back the collected issues in a journal’s catalogue should extend.

So remember: “Cited” = Cites Received and “Citing” = Cites Given, and both can give you a better picture of a journal’s staying power for archival purposes.


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