  The intention of this work is to analyze top scientists' collaboration
behavior at the "international", "domestic extramural" and "intramural" levels,
and compare it to that of their lesser performing colleagues. The field of
observation consists of the entire faculty of the Italian academic system, and
so the coauthorship of scientific publications by over 12,000 professors. The
broader aim is to improve understanding of the causal nexus between research
collaboration and performance. The analysis is thus longitudinal, over two
successive five-year periods. Results show a strong increase in the propensity
to collaborate at domestic level (both extramural and intramural), however this
is less for scientists who remain or become top, than it is for their
lower-performing colleagues. In contrast, the increase in international
collaboration behavior is greater for scientists who become or remain top than
it is for their peers. The increase in productivity by those who acquire top
scientist status is due precisely to the greater average impact of the
publications achieved in collaboration with foreign colleagues.
