American mathematicians ... 'reallocated themselves in idea space' in response to an influx of Soviet mathematicians to the United States.
Workers may not only move physically from one job to another or one geographic area to another, they may also move in the more abstract space of ideas. In Cognitive Mobility: Labor Market Responses to Supply Shocks in the Space of Ideas (NBER Working Paper No. 18614), authors George Borjas and Kirk Doran focus on American mathematicians and ask how they may have "reallocated themselves in idea space" in response to an influx of Soviet mathematicians to the United States. After the collapse of the Soviet Union in the early 1990s, nearly 10 percent of the Soviet mathematical workforce left the country. A disproportionate number of them settled in the United States.
Borjas and Doran find that this "supply shock" generated a strong response in terms of the topics studied by American mathematicians who reallocated themselves within idea space. The Americans moved to research topics and questions that did not receive a large number of Soviet émigrés. Furthermore, new entrants into the American mathematics community began to systematically avoid Soviet-style topics over the two-decade period that followed the Soviet influx.
The authors also find that the American mathematicians who moved to a different point in idea space took longer to produce their next paper than their colleagues who stayed within their comfort zones and areas of prior experience. Tenured mathematicians, and those with a high rate of output prior to the Soviet supply shock, were relatively less likely to switch fields than were the younger or less productive mathematicians.
The data used in this study included a complete tabulation of publications of all American mathematicians between 1940 and 2009, with detailed information on the field of each publication. That level of detail allowed the authors to study the evolution of research topics and interests over a particular mathematician's working life.