The Index

h-index

The h-index, or Hirsch index, measures the impact of a particular scientist rather than a journal. "It is defined as the highest number of publications of a scientist that received h or more citations each while the other publications have not more than h citations. For example, a scholar with an h-index of 5 had published 5 papers, each of which has been cited by others at least 5 times.

g-index

Proposed by Egghe in 2006 to overcome a bias against highly cited papers inherent in the h-index. The g-index is the "highest number of papers of a scientist that received g or more citations, on average"

A and R Indexes

The A and R indexes are meant to be used with h and are not stand-alone indexes. The A-index is the average number of citations per "meaningful paper". The R-index clarifies the relationship to the h-index formally.

Term and Definition

Aggregate Cited Half Life: An indicator of the turnover rate for a body of work on a subject.

Cited Half-Life: "The cited half-life is the number of publication years from the current year which account for 50% of current citations received. This figure helps you evaluate the age of the majority of cited articles published in a journal. Each journal's cited half-life is shown in the Journal Rankings Window. Only those journals cited 100 times or more times have a cited half life." (Ladwig & Sommese, 2005)

Immedicacy Index: The average number of times a journal article is cited in the year it is published. Can be useful for comparing journals on cutting edge research.

Journal Impact Factor: The journal impact factor measures the importance of a journal and "is a measure of the frequency with which the 'average article' in a journal has been cited in a particular year or period"

How Impact Factor is Calculated "The annual JCR impact factor is a ratio between citations and recent citable items published. Thus, the impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years." (from an essay originally published in Current Contents June 20, 1994)

Journal Self-Citation: "A self-citation is a reference to an article from the same journal. Self-citations can make up a significant portion of the citations a journal gives and receives each year."

Related Journals: Calculated using the number of citations from the selected journal title, total number of articles in the related journal and total number of citations from the citing journal. Uses the number of citations from one journal to another to determine a relationship.

Self-Citation: "The practice of self-citation can be considered at many levels, including author self-citation, journal self-citation, and subject category self-citation..."

Unified Impact Factor: Useful when a journal title changes because the impact factor is generally affected for two years. You can view title changes by clicking on the Journal Title changes link on one of the following pages: Journal Search, Journal Summary List, or Marked Journal List.