Time to Go? Duration Dependence in Forced Migration

In this paper we introduce some theoretical and methodological refinements to account for effects of duration dependence in forced migration flows that have not been noticed in previous research. The engine of previous theoretical arguments on forced migration has been a decision theoretic model in which the potential migrants estimate the threat to their security and then weigh this threat against costs and benefits of leaving. Moreover, in previous arguments and empirical tests the costs and benefits for relocating have been treated as being the same for all people in a country. We relax this assumption, allowing the costs and benefits of relocating to be different for different individuals. This implies that some people more readily relocate than others. Over time this generates a selection effect in the population that remains behind, such that the remaining population will become increasingly unwilling or unable to relocate. The implications of our theoretical refinement are borne out empirically. Contrary to previous research we find that the accumulated stock of forced migrants decrease rather than increase the probability of new migration. Furthermore, we find that forced migrant flows abate rather than soar over time.

本文针对此前研究未被关注的强迫移民（forced migration）流中的持续时间依赖效应（duration dependence），提出若干理论与方法论层面的改进方案。过往有关强迫移民的理论论证，核心均依托决策论模型：潜在移民首先评估自身面临的安全威胁，随后将该威胁与迁居的成本与收益进行权衡。此外，在既往的理论推导与实证检验中，迁居的成本与收益均被假定为一国之内所有个体完全相同。我们放宽了这一假设，允许不同个体的迁居成本与收益存在异质性差异。这意味着部分个体相较于其他人更倾向于且能够完成迁居。随着时间推移，这会在留守人口群体中形成选择效应：留守群体的迁居意愿与能力将逐步降低。我们的理论改进所衍生的推论得到了实证结果的支撑。与此前研究结论相悖，我们发现强迫移民的累计存量会降低而非提升新移民产生的概率。此外，我们还观察到，强迫移民流会随时间推移逐渐衰减，而非出现激增态势。