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Scholarly Communication: Impact Metrics

Impact Metrics

There are several measures of citation frequency with are used as proxies for the influence or importance of a journal.  

Impact Factor: This is a proprietary metric from Thomson Reuters.  While PSU does not have a subscription to this service, sometimes journal publishers will post a journal's impact factor on the journal's home page.  Only journals indexed in Web of Science are assigned Impact Factors.  Impact factor is the average number of citations per article for all articles published in a journal during the last two years, calculated as: 

(number of citations in 2015 to articles published in 2013 & 2014) / (total number of articles published in 2013 & 2014)

SCImago Journal Rank (SJR): A more complex calculation than Impact Factor, SJR also includes the prestige of the citing journal in its calculation (citations from prestigious journals increase a score more than those from less impactful journals.)  SJR is also calculated over a 2 year period and is includes journals from the SCOPUS database.

Eigenfactor Article Influence Score: Similar to SJR in that it incorporates the prestige of the citing journal into the calculation, this score is calculated using data from a 5-year period for journals in the Web of Science database. 

Eigenfactor Score: Scores reflects citation rates over a 5 year period and weight more heavily citations from significant journals.  However, unlike the previous 3 measures, this measure is size-dependent, meaning the score increases as the number of articles published in a journal increases.

Examples of Journal Metrics
  Impact Factor SCImago Journal Rank

Eigenfactor A.I. Score

Eigenfactor Score
Science 33.61 10.11 17.9 1.22
Journal of the American Chemical Society 12.11 5.57 3.3 .813
Applied Geochemistry 2.27 .89 .7 .014

Author Metrics

H-Index (Hirsch Index): A measure of the number and impact of papers by an author that can be calculated using the number of papers an author has published and the number of citations each paper received.   An author with an H-index of 5 has 5 papers that were cited 5 or more times.  While it can be run on any set of articles (for example, all articles from a single journal) it is most often used with reference to all publications by a single author or a group of authors.  You can use Web of Science to calculate the H-index for an author.

Article Metrics

Traditionally the most common article level metric was the citation count, which can be found in either Web of Science or Google Scholar.  Increasingly publishers are making available other article level data such as:

  • downloads
  • bookmarks
  • hyperlinks
  • comments

Book Metrics

The Open Syllabus Project by Altmetrics takes data from a large number of syllabi and captures how often books or book chapters are involved in a course, offering another way to measure the impact of a book.