The impact factor of a journal is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period.
Journal Citation Reports JCR® is the sole place where impact factors are calculated and reported. JCR® covers approximately 10,000 journal titles. This is a small minority of the journals in publication, so be aware: most journals do not have an impact factor.
The Impact factor formula
ISI defines the impact factor as a ratio of two elements: The denominator is the total number of "citable" articles published in a particular journal within a given timeframe. The numerator is the total number of citations in the current year to any article published in this journal during that given timeframe. ISI has defined this time frame as two years.
The impact factor (IF) of journal A in a particular year Y is calculated using the following formula:
Some of the main differences between the two measures:
JCR: uses Web of Science indexed journals around 10,000.
SJR: used Scopus indexed journals around 20,000.
JCR: The journal impact factor is a measure of the frequency with which the average article in a journal has been cited in a particular 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. An impact factor of 1.0 means that, on average, the articles published one or two years ago have been cited one time. An impact factor of 2.5 means that, on average, the articles published one or two years ago have been cited two and a half times.
SJR: shows the average number of weighted citations received in the selected year by the documents published in the journal in the three previous years.
There is currently no single tool/database that indexes all journals across all vendors.
Each database that offers citation analysis uses their own content and journals indexed to calculate citation analysis.
The Impact Factor of a journal is based on the "citedness" of the articles in the journal. Impact factors can be used to:
How to find the impact factor of a journal?
You can find the impact factor of a journal in a database called Journal Citation Reports of Web of Science
Select a JCR edition and year: Science citation index ( SCIE) or Social Sciences citation index (SSCI). Sometimes you may need to look at both lists.
Select an option:
The SCImago Journal & Country Rank is a portal that includes the journals and country scientific indicators developed from the information contained in the Scopus® database. These indicators can be used to assess and analyze scientific domains.
This indicator shows the visibility of the journals contained in the Scopus® database from 1996.
Scopus is the world's largest abstract and citation database of peer-reviewed literature and quality web sources, with smart tools to track, analyze and visualize research.