Impact Factor - What is it?; Why use it?
The impact factor (IF) is a measure of the frequency with which the average article in a journal has been cited in a particular year. It is used to measure the importance or rank of a journal by calculating the times its articles are cited.
How Impact Factor is Calculated?
The calculation is based on a two-year period and involves dividing the number of times articles were cited by the number of articles that are citable.
Calculation of 2010 IF of a journal:
Journal Citation Reports provides ranking for journals in the areas of science, technology, and social sciences. For every journal covered, the following information is collected or calculated: Citation and article counts, Impact factor, Immediacy index, Cited half-life, citing half-life, Source data listing, Citing journal listing, Cited journal listing, Subject categories, Publisher information.
You can enter a journal title in the Search box under "Go to Journal Profile". Because impact factors mean little on their own, it's best to view the journal you are interested in comparison to the other journals in the same category. To determine the impact factor for a particular journal, select a JCR edition (Science and/ or Social Science), year, and Categories, found on the left of the screen. Click Submit. Scroll the list to find the journal you are interested in. The list can be resorted by Journal time, Cites, Impact Factor, and Eigenfactor.
Eignenfactor scores can be found in Journal Citation Reports (listed above) or at eigenfactor.org. Journal Citation Reports or at eigenfactor.org. Eigenfactor scores are intended to give a measure of how likely a journal is to be used, and are thought to reflect how frequently an average researcher would access content from that journal. (Wikipedia) (Find out more about the Eigenfactor)
Scopus provides three journal metrics - CiteScore, SJR (SCImago Journal Rank) and SNIP (Source Normalized Impact per Paper). Once you are in Scopus, click on "Sources" at the top to access the journal impact data. See below for more on SJR and SNIP
Over 22,000 active journals from over 4,000 international publishers
“The SCImago Journal & Country Rank is a portal that includes the journals and country scientific indicators developed from the information contained in the Scopus® database (Elsevier B.V.).” Scopus contains more than 15,000 journals from over 4,000 international publishers as well as over 1000 open access journals. SCImago's "evaluation of scholarly journals is to assign weights to bibliographic citations based on the importance of the journals that issued them, so that citations issued by more important journals will be more valuable than those issued by less important ones." (SJR indicator)
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. Unlike the well-known journal impact factor, SNIP corrects for differences in citation practices between scientific fields, thereby allowing for more accurate between-field comparisons of citation impact. CWTS Journal Indicators also provides stability intervals that indicate the reliability of the SNIP value of a journal. SNIP was created by Professor Henk F. Moed at Centre for Science and Technology Studies (CWTS), University of L
CWTS Journal Indicators currently provides four indicators:
See more at: https://www.journalindicators.com/methodology