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Keep the Quick Reference Card handy for an explanation of all the metrics included in JCR.
See Thomson Reuters' Citation Impact Center for further information eg
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.
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
Impact factors can be used to:
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.