Page 184 - Becoming Metric Wise

176 Becoming Metric-Wise

journals covered by the database. As a mathematical formula DCP can be
written as follows:
n
r 1 1 r 2 1 ::: 1 r n 1 X
DCP 5 5 r j (6.17)
n n
j51
In this formula, n denotes the number of publications in the journal’s
subject field; r j denotes the number of references in the j-th publication
that appeared in the three preceding years in journals covered by the data-
base. Such reference items are called active references.

6.12.2 The New SNIP Indicator
Waltman et al. (2013) pointed out that the original SNIP indicator had
some properties which a good indicator is not supposed to have, namely:
1. It may happen that an additional citation leads to a decrease of the
SNIP-value.
2. Nonconvexity: if two journals merge (are considered as one whole)
then one would expect a new SNIP-value between the original two
SNIP-values. However, this does not have to be the case. This is a
convexity issue, see also Ramanana-Rahary et al. (2009) for a discus-
sion of convexity issues in scientometric evaluations.
For these reasons Waltman et al. (2013) proposed a revised SNIP index.
Its most significant modifications with respect to the original one are:
• Database citation potential (DCP)-values are calculated as harmonic
rather than arithmetic averages.
• The calculation of DCP values takes into account not only the num-
ber of active references in citing publications but also the proportion
of publications with at least one active reference in citing journals.
• The distinction between DCP and RDCP is abandoned, in other
words the median DCP value does not play a role anymore.
We provide now some details about the new SNIP. The basic formula
is SNIP 5 RIP/DCP in which the RIP-value of a journal is the same as
in the original version. The DCP-value is a harmonic mean:
1 n
DCP 5 (6.18)
3 1 1 1 1 ::: 1 1
p 1 r 1 p 2 r 2 p n r n
where the r j ’s have the same meaning as before, namely the number of
references in the j-th publication. The p j ’s are new entities. Consider the
jth publication in the subject field of a journal and consider then all pub-
lications that appeared in the same journal and the same year as the