Abstract
This paper first analyzes the effects of migration on the research performance of eight Japanese scientists who moved to the USA. Four of those have returned to Japan (examples of brain circulation) and the others are examples of brain drain. In both cases, the research conducted in the USA has a higher impact than research conducted in Japan when the impact was measured by the number of citations. This paper also examines the effects of the international co-authorship on citation impact. In the previous research, the effects were tested by macro data. This paper uses micro data, which enables us to control the influences of differences in scientists' capabilities. As a result, in the cases of the brain circulation, the international collaboration beyond borders increases the impact. On the other hand, all the cases of the brain drain show a negative impact on citation regarding collaborative research with Japanese scientists.
