Immediacy index

An immediacy index is a measure of how topical and urgent work published in a scientific journal is. Along with the better known impact factor measure, it is a calculated each year by the Institute for Scientific Information for those journals which it indexes; both impact factors and immediacy indices are published annually in the Journal Citation Reports.

Calculation
The immediacy index is calculated based on the papers published in a journal in a single calendar year. For example, the 2005 immediacy index for a journal would be calculated as follows:


 * A = the number of times articles published in 2005 were cited in indexed journals during 2005
 * B = the number of articles, reviews, proceedings or notes published in 2005


 * 2005 immediacy index = A/B

As with the impact factor, there are some nuances to this: ISI excludes certain article types (such as news items, correspondence, and errata) from the denominator.