*


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# Selection bias

Note:

1. Don't confuse selection bias with sampling bias.
   * **Sampling bias:** We've collected a sample that is unrepresentative of a broader population.
   * **Selection bias:** Within our sample, the people with `\(T=1\)` have different potential outcomes from people with `\(T=0\)`.

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2. Selection bias is an all-encompassing category for several sources of bias:
   - Omitted variables bias
   - Reverse causality
   - Selection on gains

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3. What is a **research design** 