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Research Impact: Measuring Impact

Provides an introduction to the various ways to measure researcher, article, and journal impact

Measuring Impact

Different tools and measures can be used to measure impact.  It is important to understand the difference between the types of impact measures and apply them appropriately.

Measures of Author Impact

  • h-index
    Proposed by J.E. Hirsch in 2005, this metric has become one of the most used metrics for measuring a researcher's impact.  However, it is much criticized, and often controversial.  The h-index is a measure of a researcher's impact that is defined as:
    • A scientist with an index of h has published h papers each of which has been cited in other papers at least h times.
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  • m-index
    ​In response to the need to facilitate comparisons between researchers with different lengths of careers, the m-index or m-quotient, tries to account for the fact that junior researchers have not had time to accumulate citations on their papers. The m-index is:
    • the h-index divided by the number of years a researcher has been active (measured as the number of years since the first published paper).
       
  • g-index
    In response to criticism that the h-index ignores the number of citations to each article beyond what is needed to achieve a certain h-index, the g-index was proposed by Leo Egghe in 2006 to give more weight to highly-cited articles. The g-index is defined as:
    • Given a set of articles ranked in decreasing order of the number of citations that they received, the g-index is the (unique) largest number such that the top g articles received (together) at least g2 citations.

Measures of Article Impact

  • Web of Science
    • Article records in Web of Science's Science Citation Index and Social Science Citation Index include the number of times the article has been cited by other items from within Web of Science products.
    • A built-in tool for calculating the h-index from an author search is available.
       
  • ​Scopus
    • Article records in Scopus include the number of times the article has been cited since 1996 by other articles.
    • A built-in tool for calculating the h-index from an author search is available.
       
  • Google Scholar
    • On the hamburger menu on the left, open Advanced Search. Enter the author's name in the appropriate field, and click search. In the search results, locate the 'Cited By' number beneath each citation.
    • Users can set up a profile which will automatically calculate the h-index and the i10-index.  
       
  • Relative Citation Ratio (RCR)
    • A field-normalized indicator of influence, used by the NIH for evaluating the relative merits of biomedical research articles.
    • The RCR is calculated by dividing the number of citations a paper received by the average number of citations an article usually receives in that field. That number is then benchmarked against the median RCR for all NIH-funded papers.
    • Use the iCite tool to find the RCR for articles published between 1995 and 2016

Measures of Journal Impact

  • Impact Factor
    • Found in Journal Citation Reports, a database produced by the same company as Web of Science.
    • The Impact Factor is calculated by dividing the number of citations in the year by the total number of articles published in the two previous years.
       
  • SCImago Journal Rank (SJR)
    • A free metric available in Scopus as well as at the SJR site.  Includes the journals developed from information contained in the Scopus database.
    • It is a measure of scientific influence of scholarly journals that accounts for both the number of citations received by a journal and the importance or prestige of the journals where such citations come from.
       
  • Eigenfactor
    • Found in Journal Citation Reports, a database produced by the same company as Web of Science as well as at The Eigenfactor Project site.
    • The Eigenfactor score is a rating of the total importance of a scientific journal.  

 

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