  International collaboration as measured by co-authorship relations on
refereed papers grew linearly from 1990 to 2005 in terms of the number of
papers, but exponentially in terms of the number of international addresses.
This confirms Persson et al.'s (2004) hypothesis of an inflation in
international collaboration. Patterns in international collaboration in science
can be considered as network effects, since there is no political institution
mediating relationships at that level except for the initiatives of the
European Commission. During the period 2000-2005, the network of global
collaborations appears to have reinforced the formation of a core group of
fourteen most cooperative countries. This core group can be expected to use
knowledge from the global network with great efficiency, since these countries
have strong national systems. Countries at the periphery may be disadvantaged
by the increased strength of the core.
