  The practice of collaboration, and particularly international collaboration,
is becoming ever more widespread in scientific research, and is likewise
receiving greater interest and stimulus from policy-makers. However, the
relation between research performance and degree of internationalization at the
level of single researchers still presents unresolved questions. The present
work, through a bibliometric analysis of the entire Italian university
population working in the hard sciences over the period 2001-2005, seeks to
answer some of these questions. The results show that the researchers with top
performance with respect to their national colleagues are also those who
collaborate more abroad, but that the reverse is not always true. Also,
interesting differences emerge at the sectorial level. Finally, the effect of
the nation involved in the international partnership plays a role that should
not be ignored.
