Impact Factor

Kate McCain MCCAINKW at DUVM.BITNET
Sat Feb 12 09:58:31 EST 1994


The Institute for Scientific Information (ISI) here in Philadelphia publishes
Science Citation Index, Social Science Citation Index, Arts & Humanitities
Citation Index, and online and CD_ROM counterparts, as well as many
specialized products.  They also compile, on an annual basis, publication
and citation statistics for the journals they index--for two of the citation
indexes SCI and SSCI; this publication is the _Journal Citation Reports_.

If you want to compare journals based on their overall visibility as reflected
by the citations their articles receive, there are two basic numbers that
you may be interested in.  The first is "total citations received to all
published articles" (otherwise known as "Raw Citation Count"). This is
obviously affected by 1) the knowledge domain; 2) the length of time the title
has been around; 3) the number of articles per issue; 4) the number of issues
per year (and many other things that we bibliometricians like to think about).
_Nature_ asserts its importance vis a vis _Science_ because its Raw Citation
Count is larger.  Nature publishes more articles per year, on the average than
Science does.

The Impact Factor adjusts for some of the size/frequency related features of
the *cited* journal (but not those making reference to the previously
published work). It is defined as the ratio: citations made to two years
worth of articles/number of articles published published over those two years.
In other words, citations per article for a two year period; usually the
two years just back from the citing year. That is, for 1993 journals, their
Impact Factor would be cauculated as # citations received for 1991 & 1992
articles/# articles published in 1991 & 1992. This levels the playing field
somewhat and gives Annual Reviews more visibility than they might otherwise
have (publishing 25-35 articles/year as compared to the several thousand
of Nature, Science, or JBC). In an Impact Factor ranking, Science ranks
higher than Nature because, though Nature received more total citations, theywe
re sperad out over more articles.

Note that the Impact Factor is an imperfect measure and that it is really
best used 1) in conjunction with other quantitative and qualitative measures
in journal evaluation and 2)to compare titles *within* a domain rather than
across domains.  There are other, more labor-intensive and specialized
quanititative citation-based measures that can inform researchers. I have
written a small monograph on the subject [   8-)   ].

If you want current Impct Factors, the best bet is to check with your local
University library and see if they receive the JCR for SCI (the main body is
on microfiche, but the data you want are included in hard copy).  I am
working at home and don't have access to my JCR.  If it is really important,
I can try to get the data for you early this coming week.

I hope this helps.

Kate McCain                         "bibliometrics R us"
College of Information Studies
Drexel UNiversity

mccainkw at duvm.ocs,drexel.edu



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