Before revision:  These conditions require a combination of assumptions that restrict both the unobserved heterogeneity in treatment assignment and how the instruments target the treatments . We introduce the concept of filtered treatment, which takes into account limitations in the analyst's information  .
After revision:  These conditions require a combination of assumptions that restrict both the unobserved heterogeneity in treatment assignment and how the instruments target the treatments , and optionally (iii) the extent to which counterfactual averages are heterogeneous. We allow for limitations in the analyst's information .