The return to big-city experience: Evidence from refugees in Denmark
利用丹麦1986-1998年间难民被随机安置到不同劳动力市场的自然实验，发现初始工资相似，但在哥本哈根的难民每增加一年经验，工资增长快35%，主要原因是工人更快地流向城市特有的企业、职业和行业。
We offer causal evidence of higher returns to experience in big cities. Exploiting a natural experiment that settled refugees across labor markets in Denmark between 1986 and 1998, we find that refugees initially earned similar wages across locations. However, those placed in Copenhagen exhibited 35% faster wage growth with each additional year of experience. Faster sorting of workers toward the type of establishments, occupations, and industries typically found in cities accounts for the vast majority of this urban wage-growth premium.