Preprint version about co-occurrence matrices

[Loet Leydesdorff]

Co-occurrence Matrices and their  <http://www.leydesdorff.net/aca/index.htm>
Applications in Information Science: Extending ACA to the Web Environment

 <http://www.leydesdorff.net/aca/aca.pdf> <pdf-version>

Loet Leydesdorff  <outbind://7/#_ftn1> [1] and Liwen Vaughan
<outbind://7/#_ftn2> [2]



Co-occurrence matrices, such as co-citation, co-word, and co-link matrices,
have been used widely in the information sciences. However, confusion and
controversy have hindered the proper statistical analysis of this data. The
underlying problem, in our opinion, involved understanding the nature of
various types of matrices. This paper discusses the difference between a
symmetrical co-citation matrix and an asymmetrical citation matrix as well
as the appropriate statistical techniques that can be applied to each of
these matrices, respectively. Similarity measures (like the Pearson
correlation coefficient or the cosine) should not be applied to the
symmetrical co-citation matrix, but can be applied to the asymmetrical
citation matrix to derive the proximity matrix which is needed for further
analysis such as multidimensional scaling. The argument is illustrated with
examples. The study then extends the application of co-occurrence matrices
to the Web environment where the nature of the available data and thus data
collection methods are different from those of traditional databases such as
the Science Citation Index. A set of data collected with the Google Scholar
search engine is analyzed using both the traditional methods of multivariate
analysis and the new visualization software Pajek that is based on social
network analysis and graph theory.


** apologies for cross-postings; comments are very welcome in this stage.
  _____


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



The Challenge of  <http://www.upublish.com/books/leydesdorff-sci.htm>
Scientometrics; The  <http://www.upublish.com/books/leydesdorff.htm>
Self-Organization of the Knowledge-Based Society



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