What have been the main trends and drivers of international migration over the last century, and to what extent have migration policies been effective in shaping the volume, direction, timing, and selection of immigration and emigration? This paper reviews the insights on migration trends, determinants and policy effects gained through the DEMIG (Determinants of International Migration) project. Questioning popular perceptions of accelerating international migration, the increase in global migration has remained proportional to the increase in world population. The main migratory shifts in the second half of the twentieth century have been directional, particularly through the decline of Europe as an area of origin and the emergence of Europe and the Gulf as new global destinations. This shift in migration movements towards Europe has been associated by an overall liberalisation of migration policies, which have increasingly focused on the selecting of migrants rather than controlling numbers per se. Most rules around legal entry, stay and exit of migrants have been relaxed, but a combination of visa and border control policies have served to prevent the entry of asylum seekers and other ‘unwanted’ migrants. Our analysis shows that it would therefore be excessive to conclude that borders are ‘beyond control’ (cf. Bhagwati 2003), and that migration policies are generally effective. Yet several ‘substitution effects’ limit or undermine the effectiveness of migration controls by (1) redirecting migration through other geographical routes and destinations (spatial substitution), (2) diverting migration through other legal and unauthorized channels (categorical substitution), (3) “now or never” migration surges in anticipation of restrictions (intertemporal substitution) and (4) discouraging return and interrupting circulation (reverse flow substitution). These expose fundamental policy dilemmas as well as the importance to look beyond migration policies. Our results show the importance of accounting for the complex and often counterintuitive ways in which structural social, economic, and political factors affect migration in mostly indirect, but powerful ways that largely lie beyond the reach of migration policies.

中文翻译：

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国际移民：趋势、决定因素和政策影响

上个世纪国际移民的主要趋势和驱动因素是什么，移民政策在多大程度上有效地影响了移民和移民的数量、方向、时间和选择？本文回顾了通过 DEMIG（国际移民的决定因素）项目获得的关于移民趋势、决定因素和政策影响的见解。质疑大众对加速国际移民的看法，全球移民的增加仍然与世界人口的增加成正比。20 世纪下半叶的主要迁徙转变是定向的，特别是通过欧洲作为原产地的衰落以及欧洲和海湾地区作为新的全球目的地的出现。移民向欧洲的这种转变与移民政策的全面自由化有关，这些政策越来越关注移民的选择，而不是控制数量本身。大多数关于移民合法入境、逗留和出境的规定已经放宽，但签证和边境管制政策的结合有助于防止寻求庇护者和其他“不受欢迎的”移民入境。我们的分析表明，因此得出边界“无法控制”（参见 Bhagwati 2003）和移民政策普遍有效的结论是过分的。然而，一些“替代效应”通过 (1) 通过其他地理路线和目的地（空间替代）重新引导移民，限制或破坏了移民控制的有效性，(2) 通过其他合法和未经授权的渠道转移移民（分类替代），（3）“现在或永远”移民潮因预期限制（跨期替代）而激增，以及（4）阻碍返回和中断循环（逆向流动替代）。这些暴露了基本的政策困境以及超越移民政策的重要性。我们的研究结果表明，考虑结构性社会、经济和政治因素以大多数间接但有力的方式影响移民的复杂且往往违反直觉的方式的重要性，这些方式在很大程度上超出了移民政策的范围。(3) “现在或永远”移民潮因预期限制（跨期替代）和（4）阻碍回归和中断循环（逆向流动替代）而激增。这些暴露了基本的政策困境以及超越移民政策的重要性。我们的研究结果表明，考虑结构性社会、经济和政治因素以大多数间接但有力的方式影响移民的复杂且往往违反直觉的方式的重要性，这些方式在很大程度上超出了移民政策的范围。(3) “现在或永远”移民潮因预期限制（跨期替代）和（4）阻碍回归和中断循环（逆向流动替代）而激增。这些暴露了基本的政策困境以及超越移民政策的重要性。我们的研究结果表明，考虑结构性社会、经济和政治因素以大多数间接但有力的方式影响移民的复杂且往往违反直觉的方式的重要性，这些方式在很大程度上超出了移民政策的范围。