Identifying the effect of treatment on the treated
Seminar Room 1, Newton Institute
In the counterfactual literature, the effect of treatment on the treated (ETT) is often
branded as the effect on the treated group. This definition of ETT is vague and poten-
tially misleading because ETT is the effect on those who would normally be treated.
A more transparent definition of ETT is given within the decision theoretic framework.
The proposed definition of ETT is used to highlight misuse of terminology in the lit-
erature and discuss the types of studies that can be used for identifying ETT. Criteria
for identifying ETT from observational data, when there are unobserved confounders,
are given. The criteria are compared to those formulated within the counterfactual