The U-Shapes of Occupational Mobility
利用丹麦全人口行政面板数据，发现大多数职业的流动性呈U形且具有方向性：低工资和高工资者都更可能离开原职业，分别转向更低或更高平均工资的职业；例外是生产率快速上升或下降的职业，只有低工资或高工资者离开。
Using administrative panel data on the entire Danish population we document a new set of facts characterizing occupational mobility. For most occupations, mobility is U-shaped and directional: not only low but also high wage earners within an occupation have a particularly large probability of leaving their occupation, and the low (high) earners tend to switch to new occupations with lower (higher) average wages. Exceptions to this pattern of two-sided selection are occupations with steeply rising (declining) productivity, where mainly the lower (higher) paid workers within this occupation tend to leave. The facts conflict with several existing theories that are used to account for endogeneity in occupational choice, but it is shown analytically that the patterns are explained consistently within a theory of vertical sorting under absolute advantage that includes learning about workers' abilities.