Journal Citation Reports (JCR), a resource from ISI Web of Knowledge, provides impact factors, or the relative impact or importance of journals. It provides quantifiable statistical data on the number of citations attributed to journals and technical reports.
Journal Impact Factor
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 or period. It can be used to provide a gross approximation of the prestige of journals in which individuals have been published, but is best done in conjunction with other considerations such as peer review, productivity, and subject specialty citation.
Using Journal Citation Reports Wisely
Citation data are not meant to replace informed peer review. Careful attention should be paid to the many conditions that can influence citation rates.