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Research Impact, Citation Analysis & Altmetrics

This guide provides information on assessing the impact of research and HSL resources available for citation analysis.

The Indexes

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 each (Schreiber, 2008a)." The h-index is included in Web of Science and Scopus. For example, a scholar with an h-index of 5 has 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" (Schreiber, 2008a).

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" (Podlubny & Kassayova, 2006). The R-index clarifies the relationship to the h-index formally (Schreiber, 2008a).

Terms and Definitions

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

"The aggregate citing half-life is calculated the same way as the journal citing half-life, and its significance is comparable. For a subject category, the citing half-life is the median age of articles cited by journal in the category in the JCR year.

For example, in JCR 2003, the subject category Geochemistry & Geophysics has a citing half-life of 9.9. That means that 50% of all articles cited by articles in Geochemistry & Geophysics journals in 2003 were published between 1994 and 2003 (inclusive)." http://admin-apps.webofknowledge.com/JCR/help/h_ctghl.htm

Altmetrics: n. Tools used to assess the impact of scholarly articles based on alternative online measures such as bookmarks, links, blog posts, and tweets. Also: alt-metrics. [Alternative + metrics.]

Citation Count: measures the impact of an article, publication, or author by counting the number of times either is cited by other works. Although this sounds simple, it is complicated by the fact that there is no single citation analysis source that covers all publications and their cited references. 

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)

Eigenfactor:  "Borrowing methods from network theory, eigenfactor.org ranks the influence of journals much as Google’s PageRank algorithm ranks the influence of web pages. By this approach, journals are considered to be influential if they are cited often by other influential journals."

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" (Schreiber, 2008a).

Google PageRank:  "PageRank evaluates two things: how many links there are to a web page from other pages, and the quality of the linking sites.PageRank evaluates two things: how many links there are to a web page from other pages, and the quality of the linking sites." (Cutts, 2009)

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 each (Schreiber, 2008a)." The h-index is included in Web of Science and Scopus. 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.

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" (Podlubny & Kassayova, 2006). The R-index clarifies the relationship to the h-index formally (Schreiber, 2008a).

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" (Thomson Reuters, 2008).

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." (Thomson Reuters, 2008)

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..."

SJR: SJR, or SCImago Journal Rank, is a measure of the scientific prestige of scholarly sources.SJR assigns relative scores to all of the sources in a citation network. Its methodology is inspired by the Google PageRank algorithm, in that not all citations are equal. A source transfers its own 'prestige', or status, to another source through the act of citing it. A citation from a source with a relatively high SJR is worth more than a citation from a source with a lower SJR.https://www.elsevier.com/solutions/scopus/features/metrics

SNIP: Source Normalized Impact per Paper (SNIP) measures contextual citation impact by weighting citations based on the total number of citations in a subject field. SNIP is the ratio of a source's average citation count per paper, and the ‘citation potential’ of its subject field. It aims to allow direct comparison of sources in different subject fields.https://www.elsevier.com/solutions/scopus/features/metrics

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.

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