The impact factor (IF) is a commonly used means to measure the importance (or rank) of a scholarly journal. The IF measures the frequency an article from a given journal has been cited in a year. The higher the number, the better the impact factor. In other words, the most reputable journals tend to have the highest impact factors.
Impact factor is calculated using a two-year period by dividing the number of times articles from that journal were cited by the number of articles from that journal that could have been cited.
For instance, the 2023 IF for a journal would be calculated as follows:
Number of citations in 2023 of articles published in 2021-22: 263
Total number of articles published in 2021-22: 52
Journal impact factor: 263 / 52 = 5.057
As a general rule of thumb, an impact factor of 10 or greater is an excellent score, with scores more than 3 are considered very good. The most reputable journals, such as The New England Journal of Medicine and Nature have very high impact factors.
The simplest way to locate most Impact Factors is by using Google. Search the complete name of the journal, followed by "impact factor" or "IF" and the current year or previous year if not yet updated.
You can also visit the journal's website. The journal will often list their impact factor on their homepage or in their "About" section.
There are a few other tools available to find impact factor information.
CiteScore is Scopus's proprietary journal metric. It measures citations or articles published of a particular year and the previous three years (four years total) divided by the total number of documents published in that journal in the same four-year period.
Scopus will display the CiteScore for a particular year on that journal's source page, along with the formula. The CiteScore displayed is for Nature.
The Eigenfactor score is a calculation based on the number of times a journal has been cited in the past five years. It also takes into account the journals these citations come from. In other words, citations from journals that are highly cited themselves have more weight than those that have fewer citations. The Eigenfactor also eliminates citations from articles from the same journal (journal self-citation).
The Eigenfactor uses the Web of Science's Journal Citation Reports (JCR). Because of this, only journals primarily in the life, medical and social sciences are calculated. The Eigenfactor score of every journal on the JCR adds up to 100. In other words, each journal's score is a proportion or percentage of the total. Because of this, the vast majority of Eigenfactor scores will be values less than 1. Prestigious journals such as Nature, PNAS and Science have scores greater than 1.
You can easily find a journal's Eigenfactor by visiting http://eigenfactor.org and searching the journal by title or ISSN.
As you can see from the results below, PNAS and Science have Eigenfactor scores over 1. The Journal of Neuroscience has an Eigenfactor score less than one, but it is still listed in the 100th percentile.
