  This paper presents a methodological framework for developing scientific
mobility indicators based on bibliometric data. We identify nearly 16 million
individual authors from publications covered in the Web of Science for the
2008-2015 period. Based on the information provided across individuals'
publication records, we propose a general classification for analyzing
scientific mobility using institutional affiliation changes. We distinguish
between migrants--authors who have ruptures with their country of origin--and
travelers--authors who gain additional affiliations while maintaining
affiliation with their country of origin. We find that 3.7 percent of
researchers who have published at least one paper over the period are mobile.
Travelers represent 72.7 percent of all mobile scholars, but migrants have
higher scientific impact. We apply this classification at the country level,
expanding the classification to incorporate the directionality of scientists'
mobility (i.e., incoming and outgoing). We provide a brief analysis to
highlight the utility of the proposed taxonomy to study scholarly mobility and
discuss the implications for science policy.
