The<unk> ,  often abbreviated IF,  is a measure of the citations to science and social science journals. It is frequently used as a proxy for the importance of a journal to its field.
The<unk>  was devised by Eugene Garfield, the founder of the Institute for Scientific Information, now part of Thomson, a large worldwide US-based publisher.<unk> s are calculated each year by Thomson Scientific for those journals which it indexes, and the<unk> s and indices are published in Journal Citation Reports. Some related values, also calculated and published by the same organization, are:
the immediacy index: the number of citations the articles in a journal receive in a given year divided by the number of articles published.
the cited half-life: the median age of the articles that were cited in Journal Citation Reports each year. For example, if a journal's half-life in 2005 is 5, that means the citations from 2001-2005 are half of all the citations from that journal in 2005, and the other half of the citations precede 2001.
the aggregate<unk>  for a subject category: it  is calculated taking into account the number of citations to all journals in the subject category and the number of articles from all the journals in the subject category.
These measures apply only to journals, not individual articles or individual scientists (unlike, say, the H-index).  The relative number of citations an individual article receives is better viewed as citation<unk> .
It is, however, possible to measure the<unk>  of the journals in which a particular person has published articles. This use is widespread, but controversial. Eugene Garfield warns about the "misuse in evaluating individuals" because there is "a wide variation from article to article within a single journal".<unk> s have a huge, but controversial, influence on the way published scientific research is perceived and evaluated.
Impact factor
Limiting factor
Medical guideline
Social dynamics
Diagnostic Criteria
Dangerous goods
Algorithm
Scientific method