|Year : 2006 | Volume
| Issue : 4 | Page : 225-226
The enigma of impact factor
Edior, IJO, PD Hinduja Hospital, Mumbai, India
B K Nayak
P. D. Hinduja National Hospital & Medical Research Centre, Veer Savarkar Marg, Mahim, Mumbai 400 016
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Nayak B K. The enigma of impact factor. Indian J Ophthalmol 2006;54:225-6
Impact factor (IF) is an important objective measure to judge the value of any scientific journal. In the absence of any other popular or practical parameter, IF assumes a significant place. In the present era, where the number of peer-reviewed scientific periodicals is more than 24,000, the librarians are under tremendous pressure while selecting the journals to subscribe due to budgetary constraints. For the same reasons, researchers are also in a dilemma while selecting the journals for sourcing information to help in their research work. Once their research is successfully completed, they would want it to be published in a good journal. The publications of the scientists and their value are scrutinized by possible employers. The librarians, researchers and employers take the help of IF in judging the value of a journal.
How was IF initiated? Impact Factor is a product of the Institute of Scientific Information (ISI) of Philadelphia, PA, which is a private company. The ISI was started in the 1950s and maintains a database of the journals registered with Science Citation Index (SCI)., The purpose of the ISI database was to create products for sale such as cross-reference literature searches as well as identification of individual researchers working on particular topics. Later, in the 1960s, Garfield and Sher developed the concept of IF. It was developed as an internal ISI index to assess the relative quality of a journal to help the company decide the inclusion of any journal in their database. Though IF has expanded its applicability, it is still used to ascertain the quality of the journal quantitatively.
What is IF? If any article had been citied many times in the literature, it can be concluded indirectly that this article had produced some impact on the researchers' community. To get a better understanding let us first look at some definitions.
Citing Journal: The journal which is citing a reference.
Cited Journal: The journal which has been cited in a reference.
Source Items: All citable articles are known as Source Items. Original articles, review articles, case reports and articles in symposium supplements are counted as source items whereas letters (except where they are actually articles such as in "Nature"), abstracts, commentaries and editorials are not counted as Source Items.
The IF of a journal for a particular year can be defined as the total number of citations in that year to the articles published in the preceding two years in that journal divided by the total number of 'source items' published in the preceding two years in that journal.
Hence, IF of a journal in 2006 = Citations received in 2006 to articles published in 2005 and 2004 in that journal/ Number of source items published in 2005 and 2004 in that journal
The IF of the previous year is published around July-August every year in the Journal of Citation Report (JCR). Let us look at the example given below:
The journal in consideration is A. The year in consideration is 2006.
X = Total number of citations in any journal in the year 2006 to the articles published in the year 2005 in Journal A.
Y = Total number of citations in any journal in the year 2006 to the articles published in the year 2004 in Journal A.
M = Total number of source items published in Journal A in the year 2004.
N = Total number of source items published in Journal A in the year 2005.
Thus, IF of Journal A for the year 2006 = X+Y/M+N
This report will appear in JCR around July-August 2007.
The calculation of IF can be biased by certain factors. One of them is the preference for English language. The inclusion of journals in the database of the ISI is also limited. Certain articles are considered more citable. For example, a review article has a potential of being cited many more times than a case report which may not be cited at all. The review article may not add anything new to the scientific literature, yet has a potential to increase the IF of a journal. A journal which does not publish case reports stands a better chance of a higher IF. A highly specialized topic of a subspecialty has a very limited scope of being cited whereas basic research articles can attract authors/researchers across a wide range of subjects. Another important cause of bias is excessive self citation, which can be either by the author or the journal. Those journals that are either available for free or online with open access policy will be read by more and hence, stand a better chance of being cited., Sometimes editors have been accused of forcing the authors to cite references from their own journal. Preference for a longer article by the editor can increase the IF as they are likely to be cited more. Editorial preference for acceptance of articles based on the possibility of attracting citations, can be considered as a possible bias.
The IF has many limitations which is apparent by the many biases mentioned above. However, the IF is journal-specific and not article- or author-specific. Just a few articles on a hot topic in a journal may raise the IF substantially. According to the ISI database, only 150 journals account for 50% of what is cited across all the journals and about 25% of all the articles published. Though some of the articles may be cited negatively, they are still counted in the calculation of IF. Even retracted articles can continue to be cited for some time. Similarly, minor citations and major citations are not given differential treatment in the calculation of IF. Citations only reflect the interest in the article by the researchers and not the usefulness or quality of articles. Therefore, a controversial article will attract many more citations. The two years window period considered in the calculation of the IF may be appropriate for hot topics but it is too less for most of the topics which are slow-moving.
Many alternate measures have been suggested due to the limitations discussed earlier. Journal to a field impact score (JFIS), adjusted impact factor, cited half life impact factor (CHAL- IF), median impact factor (MIF), impact factor point average, euro factor (EF), prestige factor and immediacy index are examples of a few alternate measures suggested to ascertain the value of a journal or publication. However, the IF is still considered the most comprehensive index for judging the quality of any journal.
Not all peer-reviewed journals are included in the ISI database. Therefore, they cannot receive an IF which is published in the JCR. Once a journal applies to be included in the ISI database, it is assessed by their editorial team. The main parameters that are assessed during this process are
1. Regularity of publication
2. Editorial team's profile
3. Whether the journal is peer-reviewed
4. The relevance and topicality of the contents
Authors are lured towards submitting their articles to journals with a higher IF. In the Indian context, if you publish in a top journal, you have arrived and conquered; if you publish in any foreign journal, you have arrived and if you publish in Indian journals, you have arrived in the wrong place. In India, a small minority of scientists (mainly in physics and chemistry) publish in top journals, while the majority settle for any foreign journal equivalent to or a shade better than a corresponding Indian journal. What drives Indian scientists to do this when most such journals are not only mediocre but also would be too scarce in Indian libraries to be read by fellow Indian scientists? However, what needs to be kept in mind by the Indian authors is the higher readability and open access policy of the Indian Journal of Ophthalmology. This allows wider dissemination of the clinical and research data of Indian authors. Another advantage is that Indian ophthalmologists would be more interested than others in the work done by Indian researchers due to the topicality of the research. The works of Indian authors published in other journals may remain restricted to the curriculum vitae of the authors as most of the Indian ophthalmologists may not have access to the full text of the articles published in these journals due to the high cost of subscription. We are making efforts to get the Indian Journal of Ophthalmology included in the SCI and will not lag behind in terms of IF. Hence, the Indian Journal of Ophthalmology should be the final destination of all researchers, especially from India.
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