Scopus's Source Normalized Impact per Paper (SNIP) versus a Journal Impact Factor based on Fractional Counting of Citations

[Loet Leydesdorff]

Scopus's Source Normalized Impact per Paper (*SNIP*) versus
a Journal Impact Factor based on Fractional Counting of Citations

*JASIST* (forthcoming); preprint available at http://arxiv.org/abs/1004.3580
Abstract: Impact factors (and similar measures such as the Scimago Journal
Rankings) suffer from two problems: (i) citation behavior varies among
fields of science and therefore leads to systematic differences, and (ii)
there are no statistics to inform us whether differences are significant.
The recently introduced SNIP indicator of Scopus tries to remedy the first
of these two problems, but a number of normalization decisions are involved
which makes it impossible to test for significance. Using fractional
counting of citations-based on the assumption that impact is proportionate
to the number of references in the citing documents-citations can be
contextualized at the paper level and aggregated impacts of sets can be
tested for their significance. It can be shown that the weighted
impact of *Annals
of Mathematics* (0.247) is not so much lower than that of *Molecular
Cell *(0.386)
despite a five-fold difference between their impact factors (2.793 and
13.156, respectively).

Loet Leydesdorff & Tobias Opthof

Amsterdam School of Communications Research (ASCoR)
Kloveniersburgwal 48, 1012 CX Amsterdam
Tel.: +31-20- 525 6598; fax: +31-20- 525 3681
loet at leydesdorff.net ; http://www.leydesdorff.net/
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