t(s)
 
 - Does our experiment work in this context on these subjects?

???

Do unit history or broader context influence our results?

We can measure to see if people have been pretreated, but sometimes we can't do that or can't know in advance

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## Scenarios

 - Discuss scenarios that deal with:
   1. Ethics
   2. Practical issues
   
 - Think about:
   - What should we do in each situation?
   - Are ethical principles violated?
   - How does the situation affect our analysis?

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