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CHAPTER 14

Impact Factor of Journal as per Journal Citation

Report and Metrics

Pulok K. Mukherjee

Impact Factor (IF) and Its Importance

The evaluation of the quality of research is important for various professional societies, individual
scientists, scholarly institutions, and funding organizations. Metrics have become a fact of life in
many, if not all fields of research and scholarship. The quality of a scientific contribution is primarily
estimated from the long-term impact that it has in science. The latter can be inferred from the
citations in scientific articles that a contribution receives. These principles have been applied in the
evaluation of scientific journals. The Impact Factor of a journal (IF), first conceived in 1955 by Eugene
Garfield, the founder of the Institute for Scientific Information (ISI), has been extensively used in the
past decades as an index of quality of scientific journals and is based on citation analysis. Although
the IF has been widely regarded as the best instrument for the evaluation of the quality of scientific
journals, it has not been spared from criticism. For a specific journal, the IF is the number of citations
for publications over the previous two years divided by the number of total citable publications in
these years (the citation window). Therefore, a journal’s impact factor is based on two elements: the
numerator, which is the number of citations in the current year to any items published in a journal
in the previous two years, and the denominator, which is the number of substantive articles (source
items) published in the same two years. Although this simplicity works to an advantage of this
method, complications arise when answers to questions such as, “What is included in the citation
window?” or “What makes a good journal impact factor?” are ambiguous. The advantages of the IF
include promoting the author while giving the readers a visualization of the magnitude of review.
The disadvantages include reflecting the journal’s quality more than the author’s work, the fact that
it cannot be compared across different research disciplines, and the struggles it faces in the world of
open access.

It is one thing to use impact factors to compare journals and quite another to use them to compare
authors. Journal impact factors generally involve relatively large populations of articles and citations.
Individual authors, on average, produce much smaller numbers of articles. The impact factor could
just as easily be based on the preceding year’s articles alone, which would give an even greater weight
to rapidly-changing fields. A less current impact factor could take into account longer periods.
Alternatively, one could go beyond two years for the source items in the denominator, but then the
measure would be less current.
All citation studies should be normalized to take into account variables such as field, or discipline,
and citation practices. Citation density and half-life are also important variables. The citation density
(mean number of references cited per article) would be significantly lower for a mathematics article
than for a life sciences article. There is a widespread but mistaken belief that the size of the scientific
community that a journal serves affects the journal’s impact. This assumption overlooks the fact that
the larger the author and article pool for citing, the larger the number of published articles to share
those citations. Many articles in large fields are not well cited, whereas those in small fields may have

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