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Journal Impact Factor, or JIF, is probably the most well known journal metric. It is calculated by a company called Clarivate and published in the Journal Citation Reports. Journal Impact Factor is an indication of how many times the average article of a journal is cited. This metric is given for specific calendar years. For example, a journal will have a Journal Impact Factor for 2016, another one for 2017, and so on.
Journal Impact Factor is usually calculated based on a 2-year period, meaning that the metric will take into account citations to articles published in that journal over the preceding two years. For example, the 2-year JIF of a journal for 2017 will take into account the citations received in 2017 by articles published in the journal in 2015 and 2016.
To summarize the formula, a journal’s 2-year JIF for 2017 will be the ratio between:
Let's say a journal published 38 articles in 2015 and 42 in 2016. In 2017, those articles received a total of 280 citations. Here's the JIF calculation:
As you can see, the journal's 2017 Journal Impact Factor will be 3.5.
Below you will find a very brief video (2:33) that further explains how JIF is calculated.
As mentioned, Journal Impact Factors are published in Clarivate's Journal Citation Reports. To access these reports, you need a subscription. However, you can also look for a journal's JIF by visiting a website called SCI Journal at https://www.scijournal.org. Once you've accessed the website, type the title of the journal you're looking for in the search box. If the journal is indexed by Web of Science, the website will provide you with its JIF and some additional information.
The SCI Journal website also provides Top 10 lists of the most prominent journals in different fields of study. This is a good way to identify top publications in your discipline.
Click here or on the image shown below to see a brief slide presentation showing what information you can obtain in SCI Journal.