The impact factor of "Journal X" is calculated by "dividing the number of all current citations of source items published in Journal X during the previous two years by the number of articles Journal X published in these two years". That is, "it is a measure of the frequency with which the ‘average article' in a journal has been cited in a particular year", or the average "citation rate" of a journal's articles.
The immediacy index of "Journal X" is calculated by "dividing the number of all current citations of current source items published in Journal X by the total number of articles Journal X published that year". That is, it is the average number of current articles in a specific journal that are cited during the year they were published. It is "a measure of how quickly the ‘average article' in a specific journal is cited", or a measure of relative "currency" of journal publications.
©MJA 1998
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© 1998 Medical Journal of Australia.
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