Compare methods

	Citation Half-Life and Literature Obsolescence	Citing vs Cited Half-Life Asymmetry
Field	Bibliometrics	Bibliometrics
Family	Process / pipeline	Process / pipeline
Year of origin	1960	1960
Originator	Robert E. Burton & R. W. Kebler; Maurice B. Line	Robert E. Burton & R. W. Kebler; Ronald Rousseau
Type	Citation-aging pipeline	Two-sided aging-comparison pipeline
Seminal source	Burton, R. E., & Kebler, R. W. (1960). The "half-life" of some scientific and technical literatures. American Documentation, 11(1), 18-22.	Burton, R. E., & Kebler, R. W. (1960). The "half-life" of some scientific and technical literatures. American Documentation, 11(1), 18-22.
Aliases	Literature Half-Life, Literature Obsolescence, Citation Aging, Literature Decay Rate	Citing-Cited Half-Life Comparison, Synchronous vs Diachronous Half-Life, Reference and Citation Age Asymmetry, Journal Temporal Profile Analysis
Related	3	3
Summary	Citation half-life measures how quickly a body of literature ages by finding the median age of the documents being cited. Borrowing the metaphor of radioactive decay, Robert Burton and R. W. Kebler proposed in 1960 that scientific literatures grow obsolete at characteristic rates, and that the half-life, the time within which half of the currently used references were published, summarizes this aging. A short half-life means a field draws mostly on recent work and old papers fall out of use quickly; a long half-life means older literature stays relevant. Maurice Line's 1970 critique drew a crucial distinction between apparent obsolescence, the decline in citations to older work, and real obsolescence, separating the genuine decline in a paper's usefulness from the statistical artifact created by the rapid growth of the literature, which makes recent years appear disproportionately important simply because there are more of them.	A journal has two half-lives, and comparing them reveals its temporal personality. The cited half-life measures the median age of the articles the journal is cited for, capturing how long its own work stays useful. The citing half-life measures the median age of the references the journal's articles make, capturing how far back its authors reach. Burton and Kebler's 1960 half-life framework supplies the median-age machinery for both, and Ronald Rousseau's work on the temporal structure of journal citations underscores that incoming and outgoing citation streams age differently. When the two half-lives diverge, the asymmetry is informative: a journal whose work is cited for many years but which itself cites only recent literature sits at a fast research front yet produces durable results, while the reverse profile marks a synthesizing or archival journal. The asymmetry is the gap between how a journal is used and how it uses the literature.