Impact Factor
The Impact Factor (IF), or more precisely Journal Impact Factor ( JIF ), German impact factor, of a journal is a bibliometric measure that indicates how often an article published in this journal article from other scientific articles per year is quoted on average. In many cases, the amount of the impact factor is largely equated with the scientific quality of a journal. However, this is an equation that certainly does not apply in this simple form. Nevertheless, in practice, the achieved impact factors are often used for the evaluation of scientific publication output.
Distinction between
By repeated renaming and more related products from multiple vendors a term accrual is appropriate. The term factor ( engl. impact factor ) generally describes the ability to measure the impact of journals. The most famous product that follows this idea is the Thomson Reuters Impact Factor (formerly ISI Impact Factor ).
For the first time had the Institute for Scientific Information ( ISI) (now part of Thomson Reuters ) calculates the impact factor of journals in the 1960s and used internally in the Science Citation Index. The impact factor is now calculated from two article databases, the Social Sciences Citation Index (for the social sciences ) and the Science Citation Index ( for medicine, engineering and natural sciences). Both databases are produced by the Institute for Scientific Information (ISI ) and are also known as Web of Science. The associated factors are accordingly in the Journal Citation Reports (JCR ) published in two editions ( Science Edition and Social Sciences Edition ). A license fee must be paid for using the Journal Citation Reports by an academic institution.
Evaluation of journals and scientists
The Impact Factor (IF) is mainly used in the natural sciences and medicine, but increasingly also in other fields. It is not suitable to compare major disciplines with many researchers and publication organs and thus higher Zitierfrequenzen with smaller disciplines. Hence, in an objective possible use of the factor that only services within a discipline, that is about thematically similar journals, may be compared. Moreover, the duration reflected while the average was an article cited, in addition to the citation the long-term importance of the individual publication. It is calculated as the half-life of an article ( Cited half-life ) also made by the ISI. In modern and fast-paced disciplines such as molecular biology, the value for most journals is under five years; in disciplines such as the biological systematics, raise their magazines a long-term claim, rather than five, often more than ten years. It is therefore a legitimate tool in the comparison of scientific publication output to multiply the impact factor with the value of Cited half-life: This is similar to the lower Zitierfrequenz in some areas of science by the longer half-life of articles.
To illustrate the magnitude of the impact factor, here are two examples of journals from the field of ecology can be mentioned. The Wiley journal Diversity and Distributions had the 2011 Impact Factor 4.83. The appearing in the journal Ecology Letters had the same publisher in 2011, however, an IF of 17.557. This, however, said nothing about the actual quality of the articles appearing therein; generally have journals with a more defined subject a lower impact factor.
Especially in the medical and scientific research directions contact scientists worldwide like the impact factor of publications in order to evaluate research performance quality - mainly because the determined number apparently promises objectivity. An additional bibliometric indicator of the quality of individual research work, which avoids some specific problems of Impact Factors, is the "Science Impact Index" (SII ). He also belongs to the citation.
The Google search engine uses similar techniques. Google used for the evaluation of web pages an algorithm that determines the frequency of links ( " quote" ) basis; see PageRank. Following this pattern Eigenfactor determines the most influential journals using the frequency of citations. However, this analysis can be manipulated.
The Impact Factor is indeed information about the frequency of citations, but not about the " craft " ( methodological ) quality of a scientific journal. Is suitable for this, the magazine review.
Meanwhile, there are several variants of the factor: In addition to the classic 2-year impact factor, Thomson Scientific has introduced a 5-year impact factor. Based on Google's PageRank are variants of the Eigenfactor score and the SCImago Journal Rank and the source - Normalized Impact per Paper ( SNIP ).
Calculation
The calculation of the Journal Impact Factor ( JIF ) takes place within a two- year span using the following formula:
It follows that there can be no such impact factor for an unexpired year. Example: A Journal in the years 2006-07 a total of 116 articles published (A), were in 2008 a total of 224 articles in this journal times cited (B ), this results in a 2008 impact factor of the journal of 1,931 (B / A).
The journals of a subject area are classified in a ranked list according to their impact factor and are comparable not only between categories within a category.
Criticism
The significance of the Journal Impact Factor is controversial. For the frequency with which a journal has been cited, are of ISI all references, regardless of whether they relate to articles, editorials, meetings, letters or Conference Proceedings, taken into account. These will be counted as a " quote" in the numerator, but not as "articles" in the denominator. Consequently magazines with many " Letters" and " Conference Proceedings " can of course have a high impact factor. Whether Selbstzitierungen, ie, citations of their own work in the calculation of the impact factor should be considered, as is currently the case, is controversial. In addition, the period of two years subject areas that need much longer time to " sinking " disadvantaged, so that a correction of the half-life of Zitierdauer (see above) seems appropriate.