Impact factor (IF) is a measure of the frequency with which the average article in a journal has been cited in a particular year. It is used to sort or rank journals by their relative importance. It is assumed that journals with high IF publish articles that are cited more often than journals with lower IF.
The most notable source for journal impact factors is the annual publication called the Journal Citation Reports (JCR) published by Thomson Scientific. Among Microbiology journals, Nature Reviews Microbiology has the highest impact factor of 60.63 in 2020.
Some journals do not consider the Impact Factor to be a reliable or useful metric to assess the performance of individual articles and do not promote impact factors. For example, PLOS supports DORA – the San Francisco Declaration on Research Assessment – and does not promote our journal Impact Factors.
Calculation of Impact Factor
Thomson defines impact factor as, “The journal Impact Factor is the average number of times articles from the journal published in the past two years have been cited in the JCR year. The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years.
A journal’s impact factor for 2020 would be calculated by taking the number of citations in 2020 to articles that were published in 2019 and 2018 and dividing that number by the total number of articles published in that same journal in 2019 and 2018.
The number of cites in a journal named X in 2020 to items published in 2019 and 2018 are 1286 and 1134 respectively.
Cites to recent items = cites in 2019 + cites in 2018 = 1286+ 1134 = 2420
The number of articles published in that journal in the same period is 61 in 2019 and 59 in 2018.
Number of recent items = 61+ 59 = 120
Impact Factor = Cites to recent items/ Number of recent items = 2420/120 = 20.16
In that case, the impact factor of journal X in 2020 is 20.16.
2-year Journal Impact Factor: The Journal Impact Factor is defined as all citations to the journal in the current JCR year to items published in the previous two years, divided by the total number of scholarly items (these comprise articles, reviews, and proceedings papers) published in the journal in the previous two years.
An Impact Factor of 1.0 means that, on average, the articles published one or two year ago have been cited one time. An Impact Factor of 2.5 means that, on average, the articles published one or two year ago have been cited two and a half times. Citing articles may be from the same journal; most citing articles are from different journals
5-year Impact Factor: The 5-year journal Impact Factor is the average number of times articles from the journal published in the past five years have been cited in the JCR year. It is calculated by dividing the number of citations in the JCR year by the total number of articles published in the five previous years.
Use of Impact Factors
- Authors use impact factors to decide where to submit their research article for publication.
- Libraries use impact factors to make collection development decisions
- Academic departments use impact factors to assess academic productivity and to make decisions on promotion & tenure of faculties.
Some Microbiology Journals and their Impact Factors in 2020
|S.N||Name of Journal||2 year Impact Factor|
|1||Nature Reviews Microbiology||60.633|
|2||Cell Host and Microbe||21.02|
|3||Annual Review of Microbiology||15.5|
|5||Microbiology and Molecular Biology Reviews||14.17|
|6||FEMS Microbiology Reviews||16.41|
|8||Trends in Microbiology||17.079|
|10||PLoS Pathogens||Does not promote IF|
|11||Current Opinion in Microbiology||7.934|
|15||Soil Biology and Biochemistry||5.29|
|16||Journal of Virology||4.501|
|19||Emerging Microbes and Infections||5.842|
|20||npj Biofilms and Microbiomes||6.769|
|22||Critical Reviews in Microbiology||7.349|
|23||Biology and Fertility of Soils||5.85|
|28||Frontiers in Cellular and Infection Microbiology||4.3|
|30||Frontiers in Microbiology||5.64|
|31||Journal of Bacteriology||3.219|