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Evidence-Based Medicine: Measuring Research Impact

Citation Metrics

Traditional scholarly metrics count publications and citations in journals, books, etc. Altmetrics are new metrics that count numbers of downloads, views, comments on scholarly websites and blogs, etc.

Some Common Scholarly Metrics

Citation Tracking - Individual author/article citation counts, i.e., the number of times an individual article or a particular author has been cited by other scholars. Such data are available froim Scopus, Web of Science, Google Scholar, PLoS, BioMed Central, and other databases. Each source may give you slightly different results.

H-index -  the value where the number of articles published by an author intersects on a graph with the number of citations for each article. For instance, an author with h-index of 10 has published 10 papers that have been cited at least 10 times each. Available on Web of Science and Google Scholar if the scholar has created a user profile, among other sources.

Journal Impact Factor (from Tomson Reuter's Journal Citation Report - measured by dividing the number of current citations a journal has in a given year by the number of articles published in the two previous years. The JIF is used to indicate the relative importance of a journal within a given field and a higher JIF is seen as providing more “authority” or “weight” to a researchers’ work. But it a journal-level metric, not an article or author level metric.

Eigenfactor - a non-commercial alternative to the JIF that represents a rating of the total importance of a scientific journal. See

Altmetrics - Measuring an article's impact in terms of its mentions in social media, blogging, and other web media.

More on Altmetrics

Altmetrics (or Article-Level Metrics) can be used to measure how scholarly articles are being shared, used, and discussed in social media and publisher sites. Altmetrics will not substitute citation counts or the h-index, but complements established article-level metric tools with emerging data sources.

Limitations of traditional metric tools are that it may take years for citations to appear. They also disregard new types of scholarly communication through blog posts, tweets, bookmarking and reference managers.

More on Journal Impact Factors

Search for Journal Impact Factors using Journal Citation Reports (Incites Platform) from Thomson Reuters (connected to Web of Science).

Search for an individual journal or select to see sets of journals by subject categories. Compare an individual journal impact factor with the Median Impact Factor for the associated subject.

Facts about Impact Factors

  • Impact Factors are only calculated for journals (not articles or researchers).
  • Impact Factors are calculated by:   
    • selecting a JCR year
    • adding the total # of citations to all items published in the two previous years that were cited in the JCR year
    • divided by the total # of citable items (articles, reviews, and proceedings) published in that two previous years 
  • Impact factors are only available from Journal Citation Reports (JCR).
  • Not every journal has an impact factor.
    • Only journals indexed ISI Citation Indexes.
  • Many subject areas in science and social science are covered in JCR.

More on the H-Index

The h-index was developed by J.E. Hirsch and published in "An index to quantify an individual’s scientific research output" PNAS 102 (46): 16569-16572 November 15 2005. The paper asks, "How does one quantify the cumulative impact and relevance of an individual’s scientific research output?"

An h-index measures the broad impact of an individual’s work, and is a method to compare authors within a discipline, especially in the sciences.  A scientist has index h if h of his or her Np papers have at least h citations each and the other (Np  h) papers have h citations each.

This metric is useful because it discounts the disproportionate weight of highly cited papers or papers that have not yet been cited.

Research Impact