Issue on page /01-Introduction-To-Causality.html

[markusloecher]

I have a comment regarding the Y notation: while you precisely define the potential outcomes $Y_{0i}$ and $Y_{1i}$ the symbols $Y_{0}$ and $Y_{1}$ show up without exact definition.
Later you write "For the treated, the observed outcome is $Y_{1}$. For the untreated, the observed outcome is $Y_{0}$."
But how exactly do you drop the index $i$ ?
I am pretty sure the answer is that $Y_{0,1}$ is a random variable whereas $Y_{0,1,i}$ is not.
But it would be nice for that to be explicitly stated.

Thanks!