Content-based and Algorithmic Classifications of Journals: Perspectives on the Dynamics of Scientific Communication and Indexer Effects

[Loet Leydesdorff]

 <http://www.leydesdorff.net/classifications/index.htm> Content-based and
Algorithmic Classifications of Journals:
Perspectives on the Dynamics of Scientific Communication and Indexer Effects

 

Ismael Rafols & Loet Leydesdorff

 

The aggregated journal-journal citation matrix—based on the Journal Citation
Reports (JCR) of the Science Citation Index—can be decomposed by indexers
and/or algorithmically. In this study, we test the results of two recently
available algorithms for the decomposition of large matrices against two
content-based classifications of journals: the ISI Subject Categories and
the field/subfield classification of Glänzel & Schubert (2003). The
content-based schemes allow for the attribution of more than a single
category to a journal, whereas the algorithms maximize the ratio of
within-category citations over between-category citations in the aggregated
category-category citation matrix. By adding categories, indexers generate
between-category citations, which may enrich the database, for example, in
the case of inter-disciplinary developments. The consequent indexer effects
are significant in sparse areas of the matrix more than in denser ones.
Algorithmic decompositions, on the other hand, are more heavily skewed
towards a relatively small number of categories, while this is deliberately
counter-acted upon in the case of content-based classifications. Because of
the indexer effects, science policy studies and the sociology of science
should be careful when using content-based classifications, which are made
for bibliographic disclosure, and not for the purpose of analyzing latent
structures in scientific communications. Despite the large differences among
them, the four classification schemes enable us to generate surprisingly
similar maps of science at the global level. Erroneous classifications are
cancelled as noise at the aggregate level, but may disturb the evaluation
locally.

 

 <http://www.leydesdorff.net/classifications/classifications.pdf> <click
here for pdf>

 
 
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Loet Leydesdorff 
Amsterdam School of Communications Research (ASCoR)
Kloveniersburgwal 48, 1012 CX Amsterdam.
Tel. +31-20-525 6598; fax: +31-842239111

 <mailto:loet at leydesdorff.net> loet at leydesdorff.net ;
<http://www.leydesdorff.net/> http://www.leydesdorff.net/ 

 

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