The Impact Factor is a Bibliometric Indicator devised by Eugene Garfield in 1955 (Garfield, 1955) in order to assess quantitatively and annually the contribution as a set that makes a magazine to the science. To do this, the magazine takes into account citations received by the set of articles, understanding that cites are a direct proof of the scientific contribution of the works.
The Impact Factor is calculated with an easy and intuitive formula; to calculate the Impact Factor of a journal in a given year (e.g. 2017), it is counted the number of cites that the magazine receives in 2017 for the articles published in its two previous years and are relativized among the number of papers that have been published in those two years.
The Impact Factor is calculated in the context of Web of Science, and more specifically to the journals indexed in the databases Science Citation Index and Social Science Citation Index, and only take into account the cites received by the population of the databases of the main set “Core Collection”. Therefore, we cannot say that a magazine has a calculated impact factor if it does not belong to these databases.
Since 1975, the Instituto de Información Científica (ISI), publishes annually reports on citation of journals of Web of Science (Journal Citation Reports) where it appears calculated the Impact Factor for each magazine and are grouped and ordered, using the indicator, by subject categories, which generates a ranking ex profeso (expressly) for the magazines for positions and quartiles for each subject area.
- Only calculates to journals indexed in Science Citation Index and Social Science Citation Index of Web of Science.
- Is very sensible to manipulations as self-cites, that is to say, a journal may corrupt its articles modifying them to get more citation, even when other similar indicators: IPP, Scimago Journal Rank, Eigenfactor, Índice H y SNIP