A Simple Approach to Effects on Durations When the Treatment Timing is Chosen
2012/11/13
研討會日期 : 2012-11-13
時間 : 14:30
主講人 : Professor Myoung-Jae Lee
地點 : Conference Room B110
演講者簡介 : Myoung-Jae Lee received his Ph.D. in Economics from University of Wisconsin-Madison in 1989. He is currently serving as Professor of Economics at Korea University. His research field is in econometrics and statistics, and labor and health economics.
演講摘要 : When a treatment unambiguously defines the treatment and control groups at a given time point, its effects are usually found by comparing the two groups' mean responses. But there are many cases where the treatment timing is chosen, for which the conventional approach fails. This paper sets up a proper causal framework for such cases to propose a simple gamma-mixed proportional-hazard approach with three durations: the waiting time until treatment, the untreated duration from the baseline, and the treated duration from the treatment timing. To implement the proposal, we use a semiparametric piecewise-constant hazard as well as a Weibull hazard with a multiplicative gamma unobserved heterogeneity affecting all three durations. Despite the three durations interwoven in complex ways, surprisingly simple closed-form likelihoods are o! btained whose maximization converges well. The estimators are applied to the same data as used by Fredriksson and Johansson (2008) for employment subsidy effects on unemployment duration to find about 11.1 month reduction.
