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Citation and Journal Metrics: Impact factors (Thomson Reuters)

About Journal Citation Reports

> Uses Web of Science data
> 8,000+ Science and 3,000+ Social Science journals
> Improved Australasian coverage
> Updated annually (usually June and July)

Journal Citation Reports Quick Reference Card

Keep the Quick Reference Card handy for an explanation of all the metrics included in JCR.

Further Information

See Thomson Reuters' Citation Impact Center for further information eg

  • understanding the Journal Impact Factor
  • new journals added to JCR.

The use of impact factors can be controversial, read Professor Roger Eston's 'Editiorial' on The impact factor: a misleading and flawed measure of research quality for his viewpoint.

What is an impact factor

JCR logo [Image source JCR database]

Journal impact factors are found in Journal Citation Reports (JCR). JCR is a unique database which is used to determine the relative importance of journals within their subject categories.

An impact factor is one measure of the quality of a journal. This is calculated by the number of citations received by the journal, from other journals within the Web of Science database.

'A journal impact factor is the average number of times that articles published in a specific journal in the two previous years (eg 1998-99) were cited in a particular year (ie 2000).'

Tree, v. 14, no. 10, Oct. 1999, p 382. 

Impact Factor Calculation



Five things to know about impact factors

  1. Not all journals have impact factors. They must be indexed in Web of Science to have an impact factor
  2. A journal has only one impact factor, but it may be listed in more than one category
  3. A journal impact factor should not be looked at in isolation, but in comparison to other journals in the same category
  4. Impact factors vary across disciplines 
  5. A five-year impact factor may also be used in some disciplines.

Impact factors can be used to:

  • identify journals in which to publish
  • identify journals relevant to your research
  • confirm the status of journals in which you have published.

But is it a good number? To state that the British Medical Journal (BMJ) has an impact factor of 14.093 is not meaningful.

It is more useful to say that BMJ’s impact factor ranks sixth of 153 journals in the field of general and internal medicine. Or to compare the journal’s impact factor of 14.093 with the aggregate impact factor for its field: 3.919

It is recommended therefore that the impact factor for a journal is not looked at in isolation. Rather, the impact factor of a journal should be compared to the impact factors for other journals within the same subject category.

For medical and health sciences, the National Health and Medical Research Council in Australia moved away from using impact factors in 2010.