The Effect of Sample Selection and Initial Conditions in Duration Models: Evidence from Experimental Data on Training
研究培训项目对参与者就业和失业持续时间的影响，发现标准持续时间模型因忽略样本选择问题而估计有偏，提出新估计量并证明培训仅通过延长就业持续时间来提高就业率。
We investigate the separate effects of a training program on the duration of participants' subsequent employment and unemployment spells. This program randomly assigned volunteers to treatment and control groups. However, the treatments and controls experiencing subsequent employment and unemployment spells are not generally random (or comparable) subsets of the initial groups because the sorting process into subsequent spells is very different for the two groups. Standard practice in duration models ignores this sorting process, leading to a sample selection problem and misleading estimates of the training effects. We propose an estimator that addresses this problem and find that the program studied, the National Supported Work Demonstration, raised trainees' employment rates solely by lengthening their employment durations.