Language and the Earnings of Immigrants
利用德国移民面板数据，发现自报语言能力存在严重测量误差，导致最小二乘法低估了口语流利度对收入的影响，且测量误差问题比未观测异质性更严重。
A number of studies have established a positive effect of migrants' language proficiency on their productivity. It has been argued that these estimates are upward-biased because of the presence of unobserved heterogeneity. To obtain an accurate estimate of language effects is important since it has potentially important implications for migration policies. Using panel data on immigrants in Germany, we show that in self-reported measures of language proficiency measurement error is substantial. Our results suggest that measurement error is a more serious problem than unobserved heterogeneity, and that Least Squares underestimates the effect of speaking fluency on earnings.