Measuring Social Environment Mobility

Individuals experience a diversity of social environments throughout their lives. When measuring the degree to which different social groups are separated from each other, this fact is often overlooked: standard segregation indices always measure spatial separation at a given point in time. These segregation indices only tell one part of the story, just like income inequality indices do not take into account the fact that individuals are mobile across the income distribution throughout their lives. This paper introduces the notion of social environment mobility (SEM) and proposes tools and a methodology to analyze it. We show that unlike income mobility, SEM cannot erase segregation in the long run, and we derive an upper bound on SEM indices. We illustrate this concept using data on segregation in French middle schools. Our results show that SEM has a fairly high equalizing effect on within-school segregation but a low overall effect due to low mobility between schools.