Journal Impact Factor is often used as an indicator of prestige or quality (though this has been the subject of controversy - see Further Reading). It can be used as part of the process of considering whether to publish in a journal, an indication of the impact of scholarship published in the journal, and can influence tenure and promotion, grants, or hiring decisions depending on the field of research.
Impact factor is generally calculated using the number of citations over number of publications for a set of years (which varies depending on the source). An example of the calculation is pictured below. The more cited a journal, the more prestige for that journal in its relative field. When using impact factors, make sure to compare the ranking of a journal to other journals in the same discipline. -- (Wikipedia entry on Impact factor)
(Image courtesy of Wikipedia entry on Impact factor)
There are three main sources for obtaining journal impact factor - Journal Citation Reports (JCR), Eigenfactor (EF), and SCImago Journal and Country Rank (SJR). There are also newer metrics, such as the CiteScore, which uses SJR and Source Normalized Impact per Publication (SNIP) to calculate a rolling annual metric, and the H5-Index, which is the five year average for the H-Index of articles in a journal. A brief description of each of these is listed below.
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The JCR provides quantitative tools for ranking, evaluating, categorizing, and comparing journals based on information in the Clarivate Web of Science database. The impact factor is one of these; it is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period. [Garfield, 2005] Journal impact factor applies only to a journal or groups of journals, but not to individual articles or individual researchers.
The impact factor of a journal in a particular year is the number of citations received in the current year to articles published in the two preceding years divided by the number of articles published in the same two years. For example, Pediatrics has a 2019 impact factor of 5.359, which means that on average each of its 2018 and 2017 articles was cited 5.359 times in 2019.
Note that Eigenfactor Metrics (Eigenfactor score and Article Influence score - see below) are available in JCR for the years 2007 and later.
How to find the Journal Impact Factor by individual journal title or by subject groupings:
Individual Journal Title:
Compare two or more journals by impact factor:
For more details see:
Eigenfactor ranks and maps scientific knowledge, according to it's website "A journal's Eigenfactor score is our measure of the journal's total importance to the scientific community." [eigenfactor.org, 2009]. Some details are outlined below:
How to find the Eigenfactor:
SCImago Journal & Country Rank (SJR) is free source that includes the journals and country scientific indicators developed from Elsevier's Scopus database. It ranks journals and compares journal citation among countries. Journals are assigned to major thematic categories as well as to specific subject categories according to Scopus Classification.
The SJR indicator expresses the average number of weighted citations received in the selected year by the documents published in the selected journal in the three previous years, --i.e. weighted citations received in year X to documents published in the journal in years X-1, X-2 and X-3.For more information, see Description of SCImago Journal Rank Indicator.
How to find journal rankings in SJR:
Note: Additional types are available, such as Book Series and Conference Proceedings.
CiteScore was launched in 2016 by Elsevier as a part of the Scopus suite of metrics. CiteScore is calculated on an annual basis, showing the average citations for a given calendar year, and is only released after that year has finished. The 2019 CiteScore was released in June 2020.
Explanation of SJR, SNIP, and CiteScore
SJR, or SCImago Journal Ranking, is based on JIF's (Journal Impact Factor) citation formula, but uses a 5-year citation count and applies an algorithm based on Google's to calculate their index (see above for further explanation on this metric).
SNIP, or Source Normalized Impact per Publication, is based on SJR, but is 'flattened' or normalized to more easily allow for direct comparison between separate disciplines.
How to find journal rankings in CiteScore:
- Information in this section was informed by Scholarly Research Impact Metrics Guide by American University.
The H5-index is created by Google Scholar, and is similar to the h-index explained in Author-level Metrics.
H5-index "It is the largest number h such that h articles published in [the past 5 years] have at least h citations each". Thus, an H5-index of 60 means that that journal has published 60 articles in the previous 5 years that have 60 or more citations each.
H5-median is based on H5-index, but instead measures was the median (or middle) value of citations is for the h number of citations. A journal with an H5-index of 60 and H5-median of 75 means that, of though 60 articles with 60 or more citations, the median of those citation values is 75.
Below is a screenshot of the top journals for Library & Information Science ranked by the H5-index.
Both the H5-index and H5-median are available in Google Scholar Metrics. Journals can be browsed by discipline (Category and/or subcategory) or searched by keyword.
Google Scholar Metrics will only display the top 20 journals for each subject category. Additionally, there is no historical data.
This section comes from the Scholarly Research Impact Metrics Library Guide published by the Library at American University.