Page 188 - Becoming Metric Wise

180 Becoming Metric-Wise

to study interdisciplinarity, in the sense that the number of categories to
which a journal belongs can be used as a basic measure of journal
interdisciplinarity.

6.13.2 Indicators Available in the JCR
In this section we present a brief overview of the indicators available in
the JCR. The JCR provides yearly values of the following indicators:
total number of received citations (in that year), the standard JIF, the
5-year synchronous impact factor, the immediacy index, the number of
published articles, the cited and citing half-life, the Eigenfactor Score and
the AIS. Very often, and maybe somewhat surprisingly, there is not much
difference between a ranking of all journals in a subject area based on JIF
(2) and on JIF(5) (see Campanario, 2011; Garfield, 1998; Leydesdorff,
2009; Rousseau, 2009a).
We have not yet given the definition of the cited and the citing half-
life in the year Y. Informally, the cited half-life of a journal in the year Y is
the median age of articles from this journal that were cited in year Y.
Roughly speaking, a cited half-life of 7 years in the year 2014 means that
the articles published in this journal during the period (2008 2014)
received half of this year’s citations. For the citing half-life the term
received citations must be replaced by references given. It has been observed
that the term half-life is actually a misnomer (Broadus, 1953; Sza ´va-
Kova ´ts, 2002) as in the scientific literature the term half-life implies an
exponential function. The terms median age of cited articles and median age
of references (or of citing articles, if cited items which are not articles are
not taken into account) would be better. As the cited and citing half-life
are actually given with one decimal we provide some more information
about their calculation.
Consider, as an example the following data for a journal in the JCR
2012 (Table 6.13).
This journal received 2138 citations in the year 2012; 15 were for arti-
cles published in the year 2012 itself, 92 were for articles published in the
year 2011 and so on. Note that when the same article has been cited sev-
eral times it is counted more than once. We see that after 6 years the
journal has received 49.2% of all its citations. Hence, the time after which
exactly 50% of all citations is received lies between 6 and 7. We use linear
interpolation to find the exact number. Using linear interpolation means
that it is assumed that citations are spread evenly over the year. The