TE? 
--
**Treated and untreated people aren't the same.**
* Means are taken over groups of people who have different potential outcomes.
- For example: People who take Advil have higher pain than those who don't.
  * Treatment effect is probably negative, but difference in means is positive.

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# Interpreting mean comparisons

Let's be more precise about the connection between the ATE and the difference in means.

First, we can rewrite these as potential outcomes:
`$$\begin{aligned}
\text{Difference in M