Skip to Main Content
UMass Chan Medical School, Lamar Soutter Library. Education. Research. Health Care. Empowering the future. Preserving the past.
UMass Chan Medical School Homepage Lamar Soutter Library Homepage

Research Impact

This guide includes information and resources on measuring the impact of scholarly works, such as citation-based and alternative metrics.

What is the Impact Factor?

The Impact Factor is a long-standing metric commonly used to evaluate journals. It is an equation calculating the average citation frequency for a given journal over a given period of time. It is a ratio of citations to citable items. Generally speaking, the higher the number, the higher the quality and prestige of the journal, although the impact factor is most useful when evaluating journals within the same discipline. 

IF equation

The journal Impact Factor was invented in the 1960s by Eugene Garfield and was intended as a tool to help librarians make selection decisions and authors identify publishing venues. Today, the Impact Factor is a propriety calculation that is available only through Thompson Reuters Journal Citation Reports. 

Pros and Cons of the Impact Factor


  • A vetted, established metric for measuring journal impact within a discipline
  • Designed to eliminate bias based on journal size and frequency


  • Individual articles makes an uneven contribution to overall Impact Factor.
  • Impact Factor does not account for certain things, things like context (postive or negative citaion) and intentionality (self-citation).
  • The metric is proprietary to and bound by the contents of the Thomson Reuters database. 
  • Citations, on which the Impact Factor is based, count for < 1% of an article's overall use

Alternatives to the Impact Factor

Eigenfactor: A measure of a journal's overall importance to the scientific community based on the origin of incoming citations over a period of time; citations from highly ranked journals are weighed more heavily. (Hosted by the University of Washington; built on Thomson Reuters bibliographic data.)

Journal Metrics: Publicly accessible metrics for journal evaluation that offer three alternative views of true citation impact of a journal. (Provided by Elsevier; built on Scopus bibliographic data.)

  • SCImago Journal Rank (SJR): Measures the scholarly influence of a journal by accounting for the number of citations as well as the prestige of the citing journals. SJR is based on the eigenvector centrality measure used in network theory. It is a size-independent measure that ranks journals based on their average prestige per article. 
  • Source Normalized Impact per Paper (SNIP): Measures the contextual citation impact of a journal by weighting the citations based on the total number of citations in a discipline. This method normalized for differences in citation practices between disciplines, so that a single citation is given greater value where citations are less frequent in that field. 
  • Impact per Paper (IPP): Measures the ratio of citations to citable items for a given journal over a given period of time. IPP is the most direct correlate to the Impact Factor, but it calculates this ration over three years rather than two and it includes only peer-reviewed scholarly papers in both the numerator and the denominator. IPP is the foundational metric for the SNIP. 

Journal Metrics Comparison Chart

journal metrics comparison chartBased on the Comparison Table of SNIP, SJR, IF, AI and JFIS in "The evolution of journal assessment," [white paper] by Journal Metrics (2011).