Impact factor (IF)

"Impact Factor is a measure of importance of scientific journals. It is calculated each year by the Institute for Scientific Information for those journals which it tracks, and are published in the Journal Citation Report. Impact Factors have a huge, but controversial, influence on the way published scientific research is perceived and evaluated. " (Wikipedia, 2005).

The impact factor is also about Internet documents, cf. Noruzi (2006).

The impact factor was invented by Eugene Garfield. It  is calculated as the number of citations in a certain year to papers in the same journal in the two years before, divided by the number of articles published in that journal in the same two years.

Hofbauer et al. (2002) introduced a new measure, the Euro-Factor^TM. “In the EUROFACTOR-database we are analyzing in a modern calculation method the value of European biomedical journals, comparing more than 500 different European journals for the needs of the European “scientific market”.
    "The Euro-Factor^TM is designed as a new tool to judge European journals under European conditions. Europe has an excellent and worldwide high respected research system. Moreover, Europe has many high quality journals. If we look from an European focus to the established journal evaluation system, we might get the impression that European journals are underestimated. If you look to the new Euro-Factor^TM list you might be very surprised by finding high quality journals, of which you have never thought that they are published in Europe. European journals are better than they appear in the international, non-European dominated comparison. Europe can be proud of its scientific achievements. In a time of European unification, it is important that Europeans have their own “scientific currency”.
    European journals are judged in a 40 years old system, made by a company in Philadelphia. As you can see in international comments, published in this book, this system is discussed controversially. Due to all the needs in Europe and the high criticism against the established evaluation, we have developed a more compatible and modern factor, the European Journal Quality Factor – the Euro-Factor^TM. "

Controversies about the IF concept:

The most serious criticism of the IF concept is probably made by Per O. Seglen (e.g., 1993, 1997). He discusses, among others, the following problems associated with the use of journal impact factors:

• Journal impact factors are not statistically representative of individual journal articles
• Journal impact factors correlate poorly with actual citations of individual articles
• Authors use many criteria other than impact when submitting to journals
• Citations to "non-citable" items are erroneously included in the database
• Self citations are not corrected for
• Review articles are heavily cited and inflate the impact factor of journals
• Long articles collect many citations and give high journal impact factors
• Short publication lag allows many short term journal self citations and gives a high journal impact factor
• Citations in the national language of the journal are preferred by the journal's authors
• Selective journal self citation: articles tend to preferentially cite other articles in the same journal
• Coverage of the database is not complete
• Books are not included in the database as a source for citations
• Database has an English language bias
• Database is dominated by American publications
• Journal set in database may vary from year to year
• Impact factor is a function of the number of references per article in the research field
• Research fields with literature that rapidly becomes obsolete are favoured
• Impact factor depends on dynamics (expansion or contraction) of the research field
• Small research fields tend to lack journals with high impact
• Relations between fields (clinical v basic research, for example) strongly determine the journal impact factor
• Citation rate of article determines journal impact, but not vice versa (Seglen, 1997).

Altmann & Gorman (1999) concluded from an Australian case study: "From the forgoing evidence it is clear that impact factors are no substitute for local use studies if one is seeking hard data to support selection and de-selection decisions for serial titles. At best impact factors might be used in conjunction with data from local use studies to offer additional support for locally-grounded decisions".

“The Impact Factor is ill conceived, intellectually and technically flawed, and misleading effort to assess the academic worth of a paper”. (Boone, 2004)

"A high impact factor does not necessarily reflect a high prestige. While many high impact journals also have a high prestige such as Nature, New England Journal of Medicine, Lancet, JAMA, Annals of Medicine, and British Medical Journal, other journals such as Diabetes have a moderate prestige despite a high impact factor of around 9."  (Hofbauer et al., 2002, p. 6).

A specific issue related to IF is to what degree open access journals have higher IF compared to restricted journals? This has been examined by, among others: Antelman (2004), Hajjem et al. (2005), Harnad & Brody (2004), Kurtz et al. (2005) and Lawrence (2001). 

Coleman, A. (2007) examined the Journal of Education for Library and Information Science (JELIS) in terms of impact factor and declining subscriptions. She found that journal value is multidimensional and citations do not capture all the facets; costs, benefits, and measures for informative and scientific value must be distinguished and developed in a fuller model of journal value.

Literature:

Altmann, K. G. & Gorman, G. E. (1999). Can impact factors substitute for the results of local use studies? Findings from an Australian case study. Collecting Building, 18(2), 90-94.

Buela-Casal, G. (2004).  Assessing the quality of articles  and scientific journals: Proposal for weighted impact factor and quality index. Psychology in Spain, 2004, Vol. 8. No 1, 60-76.

Coleman, A. (2007). Assessing the value of a journal beyond the impact factor. Journal of the American Society for Information Science and Technology, published online  18 Apr 2007

Garfield, E. (1994). The Impact Factor. Current Contents, June 20, 1994. Available: http://www.isinet.com/essays/journalcitationreports/7.html/

Seglen, P. O. (1996). Bruk av siteringer og tidsskriftimpaktfaktor til forskningsevaluering. Biblioteksarbejde, #. 48, 27-34. Click for full_text PDF

Seglen, P. O. (1997). Why the impact factor of journals should not be used for evaluating research. British Medical Journal, 314, 498-502.  http://bmj.bmjjournals.com/cgi/content/full/314/7079/497

Wikipedia, the free encyclopedia.(2005). Impact factor. http://en.wikipedia.org/wiki/Impact_Factor

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Thomson: Journal Citation Reports: http://www.isinet.com/products/evaltools/jcr/

See also: Visibility

Birger Hjørland

Last edited: 21-04-2007

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