Compare methods

	Citing vs Cited Half-Life Asymmetry	Immediacy Index
Field	Bibliometrics	Bibliometrics
Family	Process / pipeline	Process / pipeline
Year of origin	1960	1972
Originator	Robert E. Burton & R. W. Kebler; Ronald Rousseau	Eugene Garfield (ISI / Journal Citation Reports)
Type	Two-sided aging-comparison pipeline	Same-year citation-rate 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.	Garfield, E. (1972). Citation analysis as a tool in journal evaluation. Science, 178(4060), 471-479.
Aliases	Citing-Cited Half-Life Comparison, Synchronous vs Diachronous Half-Life, Reference and Citation Age Asymmetry, Journal Temporal Profile Analysis	Journal Immediacy Index, Same-Year Citation Rate, Current Citation Rate, Year-of-Publication Citation Index
Related	3	3
Summary	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.	The Immediacy Index measures how quickly a journal's articles are cited by counting the citations they receive in the very year they are published. Eugene Garfield, who created the Science Citation Index and the impact factor, introduced the immediacy index as part of the Institute for Scientific Information's journal-evaluation methodology and described it in his landmark 1972 Science paper on citation analysis as a tool in journal evaluation. While the impact factor averages citations over a two-year window, the immediacy index uses a zero-year window: it divides the citations made in a given year to that year's articles by the number of citable items published that year. A high immediacy index means a journal's work is picked up almost immediately, the signature of a fast-moving, frontier field or of journals that publish hot, rapidly cited material. It is a measure of citation speed rather than of total impact.