Revisiting the Impacts of Teachers
重新分析了Chetty等人关于教师增值测量的研究，发现教师调动与学生准备程度变化相关，导致准实验估计低估了偏差，且长期效应结果对控制变量敏感，无法得出强结论。
Chetty, Friedman, and Rockoff (2014a and 2014b) study value-added (VA) measures of teacher effectiveness. Exploiting teacher switches as a sort of quasi-experiment, the first paper investigates potential bias from student sorting to teachers, and concludes that any such bias is negligible. The second paper finds that VA scores are useful proxies for teachers ’ effects on students ’ long-run outcomes. I successfully re-produce both sets of analyses and results in data from North Carolina. But I find that teacher switching is correlated with changes in student preparedness, leading quasi-experimental estimates to understate bias in VA scores. Estimates that adjust for this indicate moderate bias. The long-run effects results are sensitive to controls and cannot support strong conclusions.