  The paper addresses the stability of the co-authorship networks in time. The
analysis is done on the networks of Slovenian researchers in two time periods
(1991-2000 and 2001-2010). Two researchers are linked if they published at
least one scientific bibliographic unit in a given time period. As proposed by
Kronegger et al. (2011), the global network structures are examined by
generalized blockmodeling with the assumed
multi-core--semi-periphery--periphery blockmodel type. The term core denotes a
group of researchers who published together in a systematic way with each
other.
  The obtained blockmodels are comprehensively analyzed by visualizations and
through considering several statistics regarding the global network structure.
To measure the stability of the obtained blockmodels, different adjusted
modified Rand and Wallace indices are applied. Those enable to distinguish
between the splitting and merging of cores when operationalizing the stability
of cores. Also, the adjusted modified indices can be used when new researchers
occur in the second time period (newcomers) and when some researchers are no
longer present in the second time period (departures). The research disciplines
are described and clustered according to the values of these indices.
Considering the obtained clusters, the sources of instability of the research
disciplines are studied (e.g., merging or splitting of cores, newcomers or
departures). Furthermore, the differences in the stability of the obtained
cores on the level of scientific disciplines are studied by linear regression
analysis where some personal characteristics of the researchers (e.g., age,
gender), are also considered.
