Journal impact factors
Journal impact factors provide a system for ranking journals according to citations. They may inform your reading of journals and help you identify where to publish a potential journal article. Impact factors are to be found in Journal Citation Reports.
To find impact factors, you need to consult Journal Citation Reports (JCR). There are two editions of JCR: science and social sciences. The science edition, which covers science, medicine and engineering, includes around 8,000 journals, whilst the social sciences edition includes around 2,600 journals. There isn't an arts & humanities edition of JCR.
If you select the science edition of JCR, you can choose groups of journals from around 170 subject categories. For the social sciences there are fewer subject categories, around 55 of them. Some broad subject categories are broken down, e.g. under computer science there are separate categories for artificial intelligence, cybernetics, hardware & architecture and information systems.
A journal's impact factor is the frequency with which an "average article" published in that journal during the two previous years was cited during the JCR year. It is calculated by dividing the number of citations during the JCR year by the total number of articles in the journal's two previous years. Impact factors are available for each year from 2000 onwards.
To display the impact factors for a group of journals by subject:
- At the JCR home page, select the appropriate JCR edition and year, and accept the default subject category option
- Link to the <Submit> button
- At the subject category section, select your subject. You can select more than one subject category by holding the control key down.
- Select <Impact Factor> as the sort option using the "View Journal Data" drop-down menu
- Link to the <Submit> button
You should see a table with abbreviated journal titles ranked by their impact factors. For example, for economics in 2010, the three top journals by impact factor are J Econ Lit, Q J Econ and Technol Econ Dev Eco.
If you link to one of the abbreviated journal titles, you will see the journal's full title and other information. From this page, you can link to an <Impact Factor Trend> button to display a graph of the journal's impact factors over the last five years.
You can return to the opening JCR screen at any time by linking to the <Welcome> button, in the top left corner of the screen.
The most familiar journal metric provided by JCR is the impact factor. However, JCR also offers several other journal metrics, including: the immediacy index, five year impact factor and Eigenfactor score. The immediacy index shows how fast articles are cited following their publication. It measures the average number of times an article in a particular journal is cited in the year it is published.
For definitions of JCR's other journal metrics, see the JCR help index.