Research impact metrics

What are Journal Metrics?

• Journal metrics use the number of articles published per year and the number of citations to articles published in that journal to rank and compare scholarly journals.
• Citation analysis is based on the premise that number of citations is an indication of the importance, popularity and prestige of a journal.
• Important papers in a broader field would garner more citations than papers in a niche area. Furthermore, there is no normalization done to account for the number of researchers within a specified field.
• Journal metrics can be useful in deciding where to publish to improve the impact of you research output.

The Metrics Toolkit is a resource for researchers and evaluators that provides guidance for demonstrating and evaluating claims of research impact. With the Toolkit you can quickly understand what a metric means, how it is calculated, and if it’s good match for your impact question.

Journal Impact Factor (JIF)  from Journal Citation Reports

Journal Impact Factor (JIF) identifies the frequency with which an average article from a journal is cited in a particular year. This is calculated by deriving the ratio between the total number of citations garnered by documents and the total number of citable documents in a journal. The time period of calculation over a two year period. Only journals that are indexed in Web of Science Core Collection will have a JIF value in Journal Citation Reports JCR

(Source : JCR, 2019)

5 year Impact Factor

• A 5-Year Impact Factor shows the long-term citation trend for a journal.
•  The 5-Year Impact Factor is calculated in the same manner as the Journal Impact Factor, except that it encompasses five cited years rather than two.

CiteScore from Scopus

SJR from SCImago Journal Rank

• The SJR is freely available on the web at www.scimagojr.com  and via Scopus and uses citation data from Scopus.
• The SJR Indicator gives higher weight to citations from high impact journals and is calculated over a 3 year period. The SJR normalizes for differences in citation behavior between subject fields.
• The SJR h-index is the journal's number of articles (h) that have received at least h citations. For example, a publication with five articles cited by, respectively, 17, 9, 6, 2, and 1, has the h-index of 3.

Eigenfactor Score

Eigenfactor measures the number of times articles from the journal published in the past five years have been cited in the Journal Citation Reports (JCR) year. 

Like the Impact Factor, the Eigenfactor Score is essentially a ratio of number of citations to total number of articles. However, unlike the Impact Factor, the Eigenfactor Score:

• Counts citations to journals in both the sciences and social sciences.
• Eliminates self-citations. Every reference from one article in a journal to another article from the same journal is discounted.
• Weights each reference according to a stochastic measure of the amount of time researchers spend reading the journal.

Google Scholar metrics

• View  top 100 publications in several languages, ordered by their five-year h-index and h-median metrics.
• The h-index of a publication is the largest number h such that at least h articles in that publication were cited at least h times each.
• The h-core of a publication is a set of top cited h articles from the publication. These are the articles that the h-index is based on. 
• The h-median of a publication is the median of the citation counts in its h-core. 
• The h5-index, h5-core, and h5-median of a publication are, respectively, the h-index, h-core, and h-median of only those of its articles that were published in the last five complete calendar years.
  Read all about Google Scholar metrics here.

Source Normalized Impact per Paper (SNIP) 

•  It is freely available at CWTS Journal Indicators and via Scopus and uses citation data from Scopus.
• It is a field normalized assessment metric. 

Facts about journal metrics

Individual articles should never be judged solely on the Impact Factor or other metrics for the journal in which an article is published.

• Citation counts alone do not indicate the quality of the citations or the publication e.g. a work may be highly cited because it is controversial; this can distort the impact factor of a journal.
• Analyses are limited to the collection indexed in the database you are using, e.g. Not all journals have an Impact Factor in JCR. 
• JCR Impact Factor based on a 2 year citation window while Scopus CiteScore is based on a 3 year citation window.
• Citations may be biased e.g. English language and review journals tend to be cited more frequently than works in other languages; authors may frequently cite their own work or the work of their colleagues.
• Review journals tend to have higher impact factors than original research journals in the same field because they tend to be cited more frequently.
• Only research articles, technical notes and reviews are “citable” items. Editorials, letters, news items and meeting abstracts are “non-citable items” and so do not contribute to Impact Factors and other metrics calculated from citation data.

The table below showcases a range of different bibliometric research metrics commonly used and their definitions. 
(Click to enlarge)