A topic in Academic Standards
What is a (legitimate) impact factor?
A journal impact factor is a numerical indicator of of journal quality. In general, the higher the number, the more prestigious the journal. However, such indices need to be used carefully, especially when comparing across fields.
The compilers of such indices keep a register of journals that they consider of sufficient quality to include.1 Once included, the compilers looks at how many citations are made of papers in that journal from across the full range of indexed journals. This is usually done within a set time period (for example – how many citations within 2 year of publication, or within 5 year of publication).
So, for example, for a journal with a 2-year impact factor of 2.3, it was found that on average each paper published is cited (by a paper in a journal which is included by the index) 2.3 times within 2 years. Some papers may not be cited at all, and others many times, but the arithmetic mean 1 across papers in the journal is considered a useful indicator.
Some journals include a range of different articles types, in which case only some may be considered. (For example, book reviews may be excluded form consideration – as a journal which publishes many short book reviews will suffer form these lowering the average citation rate for its research papers).
At the time of preparing this page (May 2022) I checked some journal webpages of trustworthy journals and found claims of the following:
| Journal | Claimed impact factors |
| Research in Science Education | 5.439 (2020) Impact factor 4.021 (2020) Five year impact factor |
| Journal of Research in Science Teaching | Impact factor:4.832 |
| Science Education | Impact factor:4.593 |
| Journal of Chemical Education | Impact Factor 2020: 2.979 |
| Chemistry Education Research and Practice | Impact factor: 2.959 |
| International Journal of Science Education | 2.241 (2020) Impact Factor 2.656 (2020) 5 year IF |
| Science & Education | 2.114 (2020) Impact factor 2.232 (2020) Five year impact factor |
| Foundations of Chemistry | 1.263 (2020) Impact factor 1.012 (2020) Five year impact factor |
As the compilers of the citation indices only include certain outputs in their calculations, these indices under-estimate the actual citations of articles (so, for example, citations in academic books and student theses are not counted.)
Dishonest reporting of impact factors
Although there are well defined ways of calculating impact factors, this does not stop some journals advertising 'impact factors' which, if they have any substantive basis, are not calculated in the ways suggested. Some predatory journals will inflate their impact factors to mislead potential authors who may be looking for somewhere to submit work. A reputable journal (such as those in the table above) will usually provide a link back to the source of their claim. The dishonest predatory journals will not actually claim to have been awarded their impact factor by the recognised source, but will either not explain where the number derived from or will refer to an alternative source based on invalid methodology. In either case, this is knowingly done to deceive, so put simply these journals lie on their websites!
Experience researchers in a field will be suspicious about a minor or unknown journal claiming similar impact factors to top journals in a field – sadly for a novice research looking to establish themselves a false impact factor may look at legitimate as a genuine one.
Read 'Publish at speed, recant at leisure'
Read 'The best way to generate an impressive impact factor is – to invent it'
Note:
1 Currently the work is undertaken by Clarivate Analytics which calculates "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" giving "a functional approximation of the mean citation rate per citable item"
