方法对比

	Immediacy Index	Source Normalized Impact per Paper (SNIP)
领域	文献计量学	文献计量学
方法族	Process / pipeline	Process / pipeline
起源年份	1972	2010
提出者	Eugene Garfield (ISI / Journal Citation Reports)	Henk F. Moed; Ludo Waltman, Nees Jan van Eck, Thed van Leeuwen & Martijn Visser
类型	Same-year citation-rate pipeline	Citation-potential-normalized journal impact pipeline
开创性文献	Garfield, E. (1972). Citation analysis as a tool in journal evaluation. Science, 178(4060), 471-479.	Moed, H. F. (2010). Measuring contextual citation impact of scientific journals. Journal of Informetrics, 4(3), 265-277.
别名	Journal Immediacy Index, Same-Year Citation Rate, Current Citation Rate, Year-of-Publication Citation Index	SNIP, Citation Potential Normalization, Source-Normalized Journal Impact, Field-Normalized Citations per Paper
相关	3	3
摘要	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.	The Source Normalized Impact per Paper, or SNIP, corrects a journal's citation rate for the citation behavior of its field so that journals in heavily cited and lightly cited disciplines can be compared on the same scale. Henk Moed introduced SNIP in 2010 with a distinctive twist: rather than classifying journals into predefined subject categories, it defines a journal's field from the bottom up as the set of papers that actually cite it, and it normalizes by that field's citation potential, measured from how long the citing papers' reference lists are. Fields whose authors cite many references generate more citations to go around, so a raw citation rate means different things in mathematics than in molecular biology. SNIP divides raw impact per paper by this citation potential to produce a field-corrected indicator. Ludo Waltman and colleagues revised the original formula in 2013 to remove some counterintuitive properties and improve stability; the revised SNIP is the version distributed in Scopus.