No interference means that my outcome is unaffected by anyone else’s treatment. Rather, my outcome is only a function of my own treatment. We’ve been using this assumption implicitly throughout this chapter. We’ll now formalize it. Assumption 2.4 (No Interference) 𝑌 𝑖 (𝑡 1 , . . . , 𝑡 𝑖−1 , 𝑡 𝑖 , 𝑡 𝑖+1 , . . . , 𝑡 𝑛 ) = 𝑌 𝑖 (𝑡 𝑖 ) Of course, this assumption could be violated. For example, if the treatment is “get a dog” and the outcome is my happiness, it could easily be that my happiness is influenced by whether or not my friends get dogs because we could end up hanging out more to have our dogs play together