Guidelines on the evidence required to support indications for listed complementary medicines
Appendix 2: Journal impact factors
The 'Impact Factor' (IF) is a measure of 'citation rate per article', and is calculated by dividing 1 years' worth of citations of a journal's articles published in the previous 2 years by the number of major articles published by that journal in those 2 years. Scientists strive to have their research published in journals with high IFs, as this has practical implications for their future funding and employment prospects.
Generally, while high IFs are indicative of the (high) quality and "impact" of research published by a given journal, low IFs do not necessarily correlate with low quality research. A given journal may for example consistently publish 'good research', but have a low IF, if the field of research is narrow and therefore has a small readership/ authorship base.
Journals with high IFs (for example Science 31, for 2011) tend to have been established for many decades, and accept manuscripts from a broad range of disciplines. Because they have a high IF, researchers attempt to publish in them first, so they get "first right of refusal" on all the best research. IF is dependent on net readership, and therefore journals that publish weekly or are free to air have higher IF value compared to journals that are published monthly, but in general a higher IF value the better the research.
As a rough rule of thumb, the following can be used to assess the potential usefulness of papers published in a journal with a given IF:
|Impact Factor Range||Implication|
|0 ("not yet available") to < 5||Ambiguous/ uninformative|
|5 to < 10||Suggestive of "quality" research (i.e. rigorous peer-review and high interest-value)|
|≥ 10||Highly suggestive of quality research|
Various companies provide IF values as well as other information of all journals to provide guidance regarding the level of quality of journals (website search for impact factors will find this information).