Page 182 - Becoming Metric Wise

174 Becoming Metric-Wise

As a disadvantage of PageRank type of indicators we note that they
enforce the Matthew effect for journals (see Subsection 9.3.2 for a discus-
sion of the Matthew effect).

6.11 THE AUDIENCE FACTOR
This indicator was introduced in 2008 by Michel Zitt with the help of
Henry Small (Zitt & Small, 2008). It is defined as follows. Consider the
journal J as a citing journal in the year Y. This journal has published arti-
cles containing reference lists going back in time. Let now m J (Y,Y 0 ) denote
the average number of references of articles published in journal J during
the publication window W(Y,Y 0 ) 5 [Y 2 Y 0 ,.. .,Y 2 1] (Y 0 . 0). This
publication window contains the so-called active references of J (as older
references are not taken into account). Now each reference is weighted by
a function depending on m J (Y,Y 0 ), namely w J (Y,Y 0 ) 5 m S (Y,Y 0 )/m J (Y,Y 0 ),
where m S (Y,Y 0 ) is the average number of active references in the whole
database (representing all sciences). In fields with shorter reference list
such as mathematics, these weights are larger than in fields that generally
have longer reference lists.
ðYÞ,is
The audience factor of journal J 0 in the year Y, denoted as AF J 0
defined as
P
ðY; Y 0 Þ
J
w J ðY; Y 0 Þ:c J;J 0
ðYÞ 5 (6.15)
AF J 0
ðY; Y 0 Þ
α J 0
ðY;Y 0 Þ represents the number of citations received by
The symbol c J;J 0
journal J 0 from journal J in the year Y for articles published (in J 0 of
ðY;Y 0 Þ denotes
course) during the publication window W(Y,Y 0 ); and a J 0
the number of articles published by journal J 0 during the period W(Y,Y 0 ).
It is clear that when all weights w are equal to one, one obtains a stan-
dard synchronous impact factor.
Properties of the audience factor are:
• It does not depend on a field’s propensity to cite.
• It does not depend on citation speed, i.e., the period between the
moment of citing and the moment of publication.
• It is independent of any journal classification scheme.
A variant of this definition, proposed in (Zitt & Small, 2008) consists
of replacing m J (Y,Y 0 )by m F (Y,Y 0 ) defined as the average number of refer-
ences in articles published in the field (or domain) F to which journal
J belongs. Again the average is determined over the publication window