signs: there is an existing resource that we want to encourage people to use (e.g., going to the library)
We want to know what effect library use has on childrens' educational outcomes.
We randomly send letters to some people encouraging them to go to the library
Not all of them do, so we have noncompliance
And some of those who do not receive letters go to the library, so we have noncompliance on both sides

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## One-sided noncompliance

`\( ITT = \overline{Y}_1 - \overline{Y}_0 \)`

`\( LATE = \frac{ITT