Citation Searching and Analysis  

Unlike common database searching by Author or Subject, citation searching tracks where works (articles, books, conference proceedings, etc) have been cited by other authors.

Citation analysis: A wide-ranging are of bibliometrics that studies the citations to and from documents. Such studies may focus on the documents themselves or on such matters as: their authors; the journals (if the documents are jornal articles) in which articles appear; the organizations or countries in which the documents are produced; the purpose of the citations. (Diodato (1994))

Citation analysis applies various techniques such as citation counts that can help establish scholarship influence and patterns.

Citation count/ citation rate/ citation frequency: often refers to the number of citations an author, document, or journal has received during a certain period of time. If expressed as a ratio, especially for a group of documents published by a particular journal, citation rate becomes equivalent to impact factor. (Diodato (1994))

Impact factor (also called journal impact factor, journal influence): A measure of the importance or influence of a group of documents. Speaking imprecisely, impact factor is the number of citations received by an average document in the group. Speaking more precisely, the impact factor is the following ratio: 

Number of citations received by the documents/ Number of documents in the group. (Diodato (1994))

The number of cited articles in a particular journal may be used to demonstrate the relative importance of that journal within a discipline or specialty area. This "journal impact factor" is tracked by ISI Journal Citation Reports; other measures (e.g. the h-index) can also be used to evaluate the impact that a journal has in its field.

Some Citation Search and  Analysis Caveats

Citation searching is a powerful tool, but it must be used with caution. Counting the number of times a publication has been cited is attractive because it is concrete data. However, citation analysis tools have extensive limitations.

Because of validity problems with citation searching, results should be used in conjunction with other indicators of quality when presented in support of a case for promotion and tenure.

Citation counts are influenced by several factors and a substantial amount of research has been published on citation analysis. See additional resources tab for some of  those publications.

Keep the following caveats in mind when evaluating research quality using citation indicators:

• No citation database can be all inclusive. Citation databases do not track citations for every journal. Journals from some fields may be poorly represented and citation results will reflect this disparity between fields.

• Some disciplines have less extensive citation activity than others. Most research work in scientific fields attracts far more citations than does research in many humanities fields.

• Recent research may not be cited. The time lag or immediacy factor varies significantly in different fields. Some scientific fields experience rapid citation at the research front, while others take years for research to be noticed.

• Citation rates can be influenced by such factors as few authors citing one another or by an author's high rates of self-citation poor quality papers may have a high citation count because they are cited while being criticized or refuted review articles, which survey a broad field of knowledge, may be cited frequently because of their breadth rather than their quality.

• Web of Science cited-reference searching works well to track citations appearing in journal articles. Citations for books, book chapters, and other types of published works are not as easily tracked by Web of Science but are well represented in Google Scholar.

• Entries in citation databases may not be standard or follow a consistent name-authority scheme. Errors made by citing authors or by indexers may make it difficult to retrieve complete citation counts.

• Common authors' name forms are very difficult to separate from other similar names (especially since many citation indexes rely on initials instead of full names). Recent advances in indexing quality, however, have improved the identification of authors' identities.

The Publish or Perish software provides an overview of the common citation metrics they include in their reports.  This can help you understand some of the common metrics often used in citation reporting.

The most common are:

Hirsch's h-index

Proposed by J.E. Hirsch in his paper An index to quantify an individual's scientific research output, arXiv:physics/0508025 v5 29 Sep 2005. It aims to provide a robust single-number metric of an academic's impact, combining quality with quantity.

Egghe's g-index

Proposed by Leo Egghe in his paper Theory and practice of the g-index, Scientometrics, Vol. 69, No 1 (2006), pp. 131-152. It aims to improve on the h-index by giving more weight to highly-cited articles.

Zhang's e-index

Publish or Perish also calculates the e-index as proposed by Chun-Ting Zhang in his paper The e-index, complementing the h-index for excess citations, PLoS ONE, Vol 5, Issue 5 (May 2009), e5429. The e-index is the (square root) of the surplus of citations in the h-set beyond h², i.e., beyond the theoretical minimum required to obtain a h-index of 'h'. The aim of the e-index is to differentiate between scientists with similar h-indices but different citation patterns.

  

Taken from: http://www.harzing.com/pop.htm#caveat