This study quantified the effects of immigration policies in an aging and depopulating Japan. Under a constant total number of immigrants, it focused on the optimal period for an immigration policy that maximized per-capita utility. Simulation results, based on an extended lifecycle simulation model with endogenous fertility, showed that a longer period immigration policy increased the future population and enhanced long-run economic growth. Conversely, a shorter period immigration policy enhanced economic growth in earlier years but less so in the long run. This study found that an optimal duration for an immigration policy, under the standard parameter settings for Japan, was nine years; this finding was derived through reconciling the merits and demerits between shorter and longer period immigration policies.

本研究量化了移民政策对老龄化和人口减少的日本的影响。在移民总数不变的情况下，它侧重于使人均效用最大化的移民政策的最佳时期。基于具有内生生育率的扩展生命周期模拟模型的模拟结果表明，较长时期的移民政策增加了未来人口并促进了长期经济增长。相反，较短时期的移民政策在早些年促进了经济增长，但从长远来看则不那么明显。该研究发现，在日本的标准参数设置下，移民政策的最佳期限为 9 年；这一发现是通过调和短期和长期移民政策之间的优点和缺点得出的。