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Impact factors: What they are, where to find them, how to use them

Review of impact factors for students at UC Merced, including information on which databases use them and their uses in thesis and dissertation writing


This guide was created in support of the Fall 2022 UC Merced Library workshop, "Impact factors: What they are, where to find them, and how to use them." Here, we'll discuss impact factors with emphasis on their use in writing theses and dissertations for degree credit at UC Merced.

What is an impact factor?

The impact factor measures the number of times a journal article has been cited by researchers in a given year. It's used to measure the importance of a scholarly journal -- that is, its importance to the discipline or field its articles cover, and by extension, the researchers working in that discipline or field -- by measuring the number of times articles in that journal are cited.


  • Generally, impact factors are the best way to determine a journal's relative importance in a particular field or discipline. Your own research will be more readily accepted if it's based on the top journals -- meaning, the journals with the highest impact factors -- in your field.
  • Impact factors are not perfect, and can be gamed, so to speak. Many journals will attempt to increase their impact factors by requiring that authors whose work is accepted for publication include citations to articles published in those journals.

Creating the impact factor

Image: University of Denver, University Libraries: Citation Analysis and Bibliometrics


  • Journal impact factors are calculated on the total number of citable articles in the two most recent, previous years. So it's not possible to get a journal impact factor for the present year. In 2022, the most recent journal impact factors will have been calculated on 2020 and 2021.
  • Because journal impact factors are calculated on two years of article citations, it's not possible to calculate an impact factor for new journals.
  • Very generally:
    • An impact factor of 10 is an excellent impact factor and indicates that the journal is of major importance in a field or discipline.
    • An impact factor of 3 is considered to be good.
    • Average impact factors for most journals are less than 1. However, this doesn't indicate that a journal is of poor quality. It may be a journal that publishes research in a field that is not noted for research.