The study of national research assessment exercises serves to evaluate the effectiveness of policies versus their objectives and to improve the formulation of future initiatives. The aim of the current study is to verify whether the introduction of the first performance-based research funding in Italy, based on the 2004-10 VQR assessment, achieved the intended objective of inducing greater international collaboration on the part of researchers. For this, we apply a bibliometric approach based on the observation of coauthorships in Italian and worldwide scientific publications over a 14-year period, beginning in the target years of the VQR assessment. Through an Interrupted Time Series Analysis, we compare the expected and observed patterns of international coauthorship for Italy and the rest of the world. Although the rate of internationalization of Italian research is seen to be increasing, whether this is a consequence of the VQR incentives, or rather part of a global phenomenon of recourse to international collaboration in response to the increasingly complex scientific challenges, it is open to interpretation.