Since a long time, Impact factor (IF) has been used as a key indicator of importance of a journal in a particular field. The founder of Institute for Scientific Information, Eugene Garfield has introduced it.
Let’s define it:
“In any given year, the impact factor of a journal is the number of citations, received in that year, of articles published in that journal during the two preceding years, divided by the total number of “citable items” published in that journal during the two preceding years.”
Impact factor (IF) of any journal can be calculated only after completing the minimum of 3 years of publication. It means it cannot be calculated for new journal which has not completed the desired period.
Example: 2018 impact factor =A/B
Where A is the number of times articles published in 2017 and 2016 were cited by indexed journals during 2018. B is the total number of citable items like articles and reviews published by that journal in 2017 and 2016. The 2018 Impact factors are actually published in 2019.
In this case, Impact factor can be calculated once all of the 2018 publications have been processed by the indexing agency.
Significance and limitation of Impact factor:
- Most frequent use of impact factor is in academic evaluation (in Universities and research institutes). It gives a general idea for public about prestige of journals.
- It is quite useful in clarifying the significance of absolute (or total) citation frequencies.
- It eliminates one important bias which tends to favor large journals over small ones, or frequently issued journals over less frequently issued ones. It also reduces the bias of selecting older journals over newer ones.
- Inclusion of review articles or letters can influence a journal’s impact and its ranking in journal lists. Review articles generally are cited more commonly than typical research article thus impact factor may get increased.
- Limitation of completion of 3 years of publication.
Agency which calculate the Impact factors: Clarivate Analytics
This agency began to publish Journal Citation Reports (JCR) in 1975 as part of the SCI (Science Citation Index) and the Social Sciences Citation Index (SSCI).
“The JCR provides quantitative tools for ranking, evaluating, categorizing, and comparing journals. Some of the journals listed in the JCR are not citing journals, but are cited-only journals. This is significant when comparing journals by impact factor because the self-citations from a cited-only journal are not included in its impact factor calculation (impact factor without self-citation).”
- It is important to note that all journals are Not tracked in the JCR database. It means those journal do not have impact factor (IF)
- Young or new journals has to wait until they have a record of citations before even being considered for inclusion
- We cannot be 100 percent sure about scientific worth of an individual article or research by just looking the impact factor.