Post-treatment problems: What can we say about the effect of a treatment among sub-groups who (would) respond in some way?
处理后分组问题:如何分析会对处理作出特定反应者的效应
Investigators are often interested in how a treatment affects an outcome for units responding to treatment in a certain way. We may wish to know the effect among units that, for example, meaningfully implemented an intervention, passed an attention check, or demonstrated some important mechanistic response. Simply conditioning on the observed value of the post-treatment variable introduces problematic biases. Further, the identification assumptions required of several…