ne if cluster means are similar
 
 - Otherwise, clustering introduces inefficiencies
 
 - Or we can change our unit of analysis
   - Contrast people as units versus clusters as units
 
???

Greater variance across clusters makes the design less efficient

Solutions:
 
 1. Add more clusters
 2. Make clusters as homogeneous as possible
 
Increasing cluster size has a negligible effect on inference



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## Pretreatment

 - An experiment involves:
 
   1. Units
   2. Treatment(s)
   3. Outcome(s)
   4. Contex