Filling the Gaps: Vacancy Chains and Agent-Based Models

This paper introduces a demographic agent-based model of mobility in opportunity structures featuring vacancy chains, such as jobs in bureaucracies or homes in residential housing systems. The novel computational treatment of vacancy dynamics is superior to analytic variants by enabling us to 1) model off-equilibrium situations; 2) simulate multiple, overlapping, exogenous shocks of varying duration and intensity; 3) instantiate dynamic systems with an inherent tendency towards stability; 4) refine theory through pattern-oriented modelling; 5) increase realism by relaxing standard Markovian assumptions of embeddedness, homogeneity, and stationarity; and 6) generate confidence bands for point estimates. Parametrising these computational vacancy models with empirical data on professional mobility among judges in a post-revolutionary context reveals an unexpected career mechanism, the purge boomerang. Meta-theoretically, this paper furthers computational ABMs by introducing a model that explicitly codes vacancies as agents, a formalisation of absence akin to the zero symbol in arithmetic.