garfield at codex.cis.upenn.edu

[Eugene Garfield]

GREGOR B. E. JEMEC : ccc2845 at vip.cybercity.dk

 TITLE      Impact factor to assess academic output
 AUTHOR     Jemec GBE
 JOURNAL    LANCET  358 (9290): 1373-1373 OCT 20 2001

 Document type: Letter
 Language: English
 Cited References: 0
 Times Cited: 0


 Addresses:
 Jemec GBE, Roskilde Hosp, Dept Med, Div Dermatol, DK-4000 Roskilde, Denmark
 Roskilde Hosp, Dept Med, Div Dermatol, DK-4000 Roskilde, Denmark

 Publisher:
 LANCET LTD, LONDON

 IDS Number:
 484RC

 ISSN:
 0140-6736

Gregor B.E. Jemec, MD, D Med Sci
Div of dermatology, dept of medicine
Roskilde Hospital
DK-4000 Roskilde
Denmark

Tel. +45 4630 2714/2742
Fax. +45 4630 2727
E-mail: ccc2845 at vip.cybercity.dk




Correspondence
Division of Dermatology, Department of Medicine, Roskilde Hospital, DK-4000
Roskilde, Denmark
(e-mail:ccc2845vip.cybercity.dk)

________________________________________________________________

LANCET  358 (9290): 1373-1373 OCT 20 2001

The Lancet


                      Impact factor to assess academic output


                      Sir--Bibliometeric analyses are a useful way to assess
academic output. Emphasis is commonly placed on impact  factor--ie, the
measure of how frequently reports in a given journal are cited. Proponents
and opponents continue to have   heated discussions on this topic.

                      The journals with the highest impact factors in each
field are an attractive target for many workers. Aficionados interpret the
study of impact factors as a relevant assessment of the state of affairs in
the different branches of medicine.

Sometimes the results of such comparisons are, however, surprising, such as
the difference between immunology  journals (maximum impact factor 37·796)
and those for rheumatology (6167·0). The development of immunology has
meant that rheumatology might be seen as a practical form of immunology, and
the difference in bibliometric weighting is therefore not easily understood.

                      Many complex factors play a part in the citation
intensity of a given journal, such as quality, circulation, and
accessibility, and much attention has been devoted to these factors. One
obvious factor has, however, been missed: the opportunity for  citation. To
assess this feature at random, we studied an ISI Journal Citation Report
(JCR) more closely. We investigated the impact factors for the top journals
in the different specialties, as defined by the ISI JCR, 1997. The number of
journals in each specialty correlated significantly with the top impact
factor achieved (Spearman's rank correlation r=0·7692 [95%  CI
0·5211-0·8974], p<0·0001). When we assessed only dermatology journals, we
noted a similar correlation for top and
 mean impact factors for the period 1991-2000.

                      This finding suggests that the number of journals per
specialty is a strong confounding factor in the determination of
traditional or basic impact factors. The difference in the number of
journals (117 vs 18) might, therefore, alter basic impact factors, for
example for immunology and rheumatology disproportionately.

                      To assess this effect, we calculated weighted impact
factors by dividing basic impact factors by the number of journals in the
specialty. Differences between specialties are not fully accounted for, but
the weighted impact factors of clinically related specialties seem more
similar for basic impact factors. Weighted impact factors, therefore, seem
to offer a more appropriate measure for comparisons than do basic impact
factors.

                      Top journals should welcome and encourage new
publishers, since more journals means a higher top basic impact factor.

                      Gregor B E Jemec
                      Division of Dermatology, Department of Medicine,
Roskilde Hospital, DK-4000 Roskilde,
                      Denmark .
                      (e-mail:ccc2845vip.cybercity.dk)