The impact factor is the average number of times articles of a journal have been cited over the past two years.
This factor is calculated annually for journals registered at the Thomson Reuter’s annual Journal Citation Reports (JCR), and is announced at the end of each year for the journals indexed in the ISI. This index is the most important indicator of the scientific evaluation of journals.
Immediacy index is calculated the same way as the impact factor. The difference is that in the immediacy index, the current year is important, and the previous years exert no effect on this index.
Cited half-life estimates all of the cites of a publication (across all cited years) during the JCR year. Therefore, a high cited half-life of a journal is indicative of its higher scientific stability and credibility