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Metrics, Citations, and Impact Factors

Information about citaion analysis, impact factors, altmetrics, and other ways to gauge the influence of scholarly work.

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Metrics are a set of methods for analyzing the impact of scholarly literature.  Citation analysis and impact factors are respected evaluation methods in academia, but as technology advances and leads to new dissemination methods for scholarly research, altmetrics have also gained prominence.

It is wise for researchers to understand these analyses for the following reasons:

  1. They can help you decide where to publish your research.
    Journals with high impact factors or other citation analysis scores are generally regarded as more prestigious and likely to reach a wider audience.
  2. They can affect your reviews and/or bids for tenure.
    Tenure committees will often evaluate a candidate's work based on where it's been published.  Candidates need to know how to defend their publication choices--especially if they choose to publish in less prestigious journals.  Understanding how various metrics are calculated can help scholars who find themselves called to defend their research.
  3. Figures can vary widely between fields.
    Different fields have different citation practices, and a journal's scores should only be compared with others in that discipline. Niche journals with small audiences may have lower scores because they don't make a big impact on the entire scholarly community, but may be valuable within their small field.


Below are brief definitions for a number of common metrics used to describe scholarly publications. For further information, you may also want to check out the Metrics Toolkit, which can help you to quickly understand what a metric means, how it is calculated, and if it’s good match for your impact question.


Altmetrics:  Alternative metrics, often an article level, that don't rely on number of citations but on factors such as webpage views and social media mentions.

Article Influence Score:  A measure of the per-article citation influence of a journal, as measured by Eigenfactor. 

Citation analysis:  A practice by which the works of an author or the articles published in a specific journal are examined to see how frequently they are cited by others and in what kinds of publications. 

Cited half-life:  The median age of the cited articles from a particular journal each year.

Eigenfactor Score:   An attempt to measure a journal's importance to the scholarly community by considering the origin of citations of that journal's content.  It is influenced by the size of the journal (so that journals that publish more articles per year have higher scores).  

g-index:  If a set of articles is ranked from most to fewest citations received, the g-index is the unique largest number such that the top g articles together received at least gcitations.  For example, a g-index of 3 indicates that the top 3 most cited articles by an author together received at least 9 citations.

h-index:  The largest number h such that publications have at least citations.  For example, an h-index of 10 indicates that the author has 10 articles that have each been cited at least 10 times. Sometimes called the Hirsch index.

i10-index:  The number of publications by an author or in a journal that have at least 10 citations.

Immediacy index:  The number of citations that articles in a journal receive in a given year divided by the number of articles published.

Impact factor:  A measure reflecting the average number of citations per article published in a journal. Impact factors are calculated using citation data for articles published in the previous two years, i.e. the 2018 impact factor for a journal would be calculated from articles published in 2016 and 2017. Specifically, it would take the number of times that articles published in 2016-2017 were cited in 2018, and divide by the total number of articles published in 2016-2017.

SJR indicator:  A measure of the influence of academic journals that considers both the number of citations received by a journal and the prestige of the journals making those citations.  Citations from more prestigious journals are ranked more highly than others.