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University of Deusto



What is the Impact Factor?

The impact or index factor measures the average number of citations to articles in scientific literature.


What is the Impact Factor used for?

It is used to compare publications and determine the relative importance of a journal in its field.

Authors use it to identify the most important journals, decide on the publication of articles and confirm the status of the journals they have published their work in.

Professors, researchers and students use it to find important information in their specialist areas.

Libraries use it to decide whether to include journals in their collections.


How is the Impact Factor calculated?

The Impact Factor is the result of the number of times articles published were cited by indexed  journals divided by the number of citable items.The most widely used formula is:

The average number of citations to those papers published in the two preceding years divided by the number of articles published in those two years.  For instance:

 2008 Impact factor: the number of times articles published in 2006 and 2007 were cited by indexed journals during 2008.


Where can you find the Impact Factor?

Journal Citation Reports:

This is a basic tool used  to consult the impact factor of a journal.  It is calculated each year by the Institute for Scientific Information for those journals it indexes.

There are two editions:

  •  JCR Science Edition (journals from the field of science).
  •  JCR Social Science Edition (journals from the field of social sciences).

Manual of Journal Citation Reports

Other analytical resources:

Since the data furnished by the Journal Citation Reports refers mainly to English speaking countries and journals in English, similar resources have been created to measure the impact factor of journals and citations not analysed by the ISI:


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