The impact factor is used to compare different journals within a certain field. The ISI Web of Knowledge indexes more than 11,000 science and social science journals.
The impact factor, a numerical score that claims to rank the
importance of scientific journals, may be resulting in unnecessary
pressure on researchers to publish in journals with high values for that
score.
With some qualifications, the impact factor is a measure
of the average number of citations for papers published in a particular
journal. It is calculated by counting the total number of citations
papers in the journal receive, and dividing by the number of papers
published in the journal. These statistics are compiled by the Institute
for Scientific Information (ISI).
Does the impact factor provide
an accurate measure of a journal’s importance? In counting citations,
only papers published in the past two years are considered, though many
research papers may be influential for much longer than two years. Also,
items such as news articles and editorials that some journals publish
are not counted in the denominator of the impact factor, but citations
to those news articles may be included in the numerator, inflating the
impact factor of journals that publish those types of articles.
Review articles, such as those published in Reviews of Modern Physics,
are often much more highly cited than the average original research
paper, so the impact factor of review journals can be quite high.
In
some fields, there have been reports of journals that have raised their
impact factors by such tactics as adding news articles, accepting
papers preferentially that are likely to raise the journal’s impact
factor, or even asking authors to add citations to other articles in the
journal.
APS journals have not been much affected by these types
of problems, said Martin Blume, APS Editor-in-Chief. In fact, Blume
says he makes a point of trying not to pay attention to the impact
factor.
Blume and others are more concerned that in some cases
hiring and tenure committees or funding agencies may use the impact
factor inappropriately as a way to evaluate individual researchers.
“There is no quantitative metric of excellence. High impact factor
journal publication is not a measure of excellence of the individual,”
said Blume.
Ivan Schuller of UCSD says he likes to publish in the Physical Review journals, because he wants his work to be read by physicists. But some of his students feel that publishing in Physical Review instead of Science or Nature,
which have higher impact factors, puts them at a disadvantage when
applying for jobs. They believe some universities may simply look at the
impact factors of journals they’ve published in, rather than carefully
review the individual’s work.
Paul Kwiat of the University of
Illinois recently co-authored a paper on quantum computation that was
published in Nature. But the impact factor, which Kwiat had never heard
of, wasn’t considered in the decision of where to publish.
"We chose Nature
because we thought we had an item that might have some general public
interest, while being novel science," Kwiat said. "I'm not sure I know
any kind of quantitative 'impact factor', but surely scientists know
that some journals are more prestigious than others, partly in view of
the difficulty of getting published in them."