Journal Citation Report (JCR): The journal-level metric is designed to demonstrate a journal's importance in a given field. Note that the Journal Impact Factor will include self-citations in its metrics and it only gives data journals indexed in Web of Science. The Impact Factor is only calculated for journals more than 5 years old.
The formula for JCR is:
A= the number of 2012 cites to articles published two years before (2010-2011)
B= the total number of articles published during a two-year span (2010-2011)
A/B = Impact factor for a journal (only for 2012)
Eigenfactor rates journals on citation influence, which is a metric based on how a journal links a researcher to another journal. Eigenfactor includes more sources, not just journal articles, and citations from highly ranked journals get a high value. However, large journals may have higher Eigenfactors simply because of their size.
Article Influence scores provide an indication of the relative importance of the influence of each of a journal's articles. AI Scores are calculated by dividing the Eigenfactor by the fraction of articles published by the journal. That fraction is normalized so that the sum total of articles from all journals is 1; therefore, scores above 1.0 indicate higher than normal influence, and scores lower than 1.0 indicate less than normal influence.
Both the Eigenfactor and the Article Influence score are only based on citations from issues of the journal that were published within the past five years.
Publish or Perish is a downloadable software program developed by Ann-Wil Harzing, that retrieves and analyzes academic citations. It uses Google Scholar and Microsoft Academic Search to obtain the raw citations, then analyzes these and presents a variety of metrics, including H-index and number of citations.
Publish or Perish can be used to determine Author Impact or Journal Impact. Results can be exported to Excel.
SCImago Journal Rank (SJR) is a weighted citation score of journals that can be found in the Scopus database.
The metric obtained from SJR is based on the following: number of journals in the database, the number of papers from a journal in the database, the number of citations. Larger journals would have a higher weight, as a result, but the number of important works normalizes this figure.
See this image for an example of the Journal Impact Factor (at 2 years) and the SJR metric (at 3 years) for a comparison of how the ratings can vary due to distinction in rules of measurement:
Aims To Provide Comparisons of Sources in Different Disciplines
Source-Normalized Impact per Paper (SNIP) measures contextual citation impact by weighting citations based on the total number of citations in a subject field. The impact of a single citation is given higher value in subject areas where citations are less likely, and vice versa.
SNIP aims to allow direct comparison of sources in different subject fields. SNIP ranks the journal based on citation analysis but also adjusts for the frequency of citations of other journals within the field (definition of "field"--all the journals that are citing this particular journal).
SNIP values may be viewed on Scopus or at the CWTS website.