Page 187 - Becoming Metric Wise

179
Journal Citation Analysis

scientific literature of 1974. We note that before the official launch of the
JCR a preliminary version had been available as computer printouts based
on 1969 data. This explains why one finds use of the JCR in the litera-
ture, before the year 1976 (Inhaber, 1974). At first the JCR were printed
as a volume of the SCI and the SSCI (but with considerable delay), later
they became available on microfiches, then on CD-ROM and more
recently as part of the InCites platform. The A&HCI has no accompa-
nying JCR.
The complete matrix of all journal citation relations is very sparse,
and hence consists largely of empty cells. Any given journal does not cite
the large majority of the other journals in the database (this observation
holds for any database of this type, not only for the JCR). If a journal
cites another one exactly once this is usually not shown in the JCR.
Taking this restriction into account, approximately 97% of all cells in a
journal-journal citation matrix are empty (Leydesdorff & Jin, 2005).

6.13.1 WoS Categories
Journals included in the JCR are assigned to subject categories (SCs) of
science, including a category Multidisciplinary Sciences. In this mixed
group one finds top journals such as Science, Nature and the Proceedings of
the National Academy of Sciences USA, but also journals with a much lower
impact factor such as National Academy Science Letters India and the
Johns Hopkins APL Technical Digest. One of the categories in the social
sciences is Information Science and Library Science. Assignment of
journals to categories is not unequivocal as journals may be assigned to
more than one subject category. This is illustrated in Table 6.12.
This table shows that more than 40% of all journals are assigned to
more than one subject category. Overlap between subject categories is a
form of cooccurrence. This aspect has been used by (Morillo et al., 2003)

Table 6.12 Division of journals over JCR SCIE subject
categories (for the year 2015)
6 SCs 6 journals
5 SCs 25 journals
4 SCs 172
3 SCs 820
2 SCs 2765
1 SC 4989