  The purpose of this paper is to apply and evaluate the bibliometric method
Bradfordizing for information retrieval (IR) experiments. Bradfordizing is used
for generating core document sets for subject-specific questions and to reorder
result sets from distributed searches. The method will be applied and tested in
a controlled scenario of scientific literature databases from social and
political sciences, economics, psychology and medical science (SOLIS, SoLit,
USB Koeln Opac, CSA Sociological Abstracts, World Affairs Online, Psyndex and
Medline) and 164 standardized topics. An evaluation of the method and its
effects is carried out in two laboratory-based information retrieval
experiments (CLEF and KoMoHe) using a controlled document corpus and human
relevance assessments. The results show that Bradfordizing is a very robust
method for re-ranking the main document types (journal articles and monographs)
in today's digital libraries (DL). The IR tests show that relevance
distributions after re-ranking improve at a significant level if articles in
the core are compared with articles in the succeeding zones. The items in the
core are significantly more often assessed as relevant, than items in zone 2
(z2) or zone 3 (z3). The improvements between the zones are statistically
significant based on the Wilcoxon signed-rank test and the paired T-Test.
