oncompliance
   - One-sided (failure to treat)
   - One-sided (control group gets treated)
   - Cross-over
 
 - Missing data

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## Analysis of data with attrition

Considerations:

 - Symmetric, possibly random, attrition
 
 - One-sided or systematic attrition
 
 - Pre-treatment/post-treatment
 
 - Pre-measurement/post-measurement
 
???

Statistically, as soon as one unit leaves study, it is no longer an experiment! Yet, we cannot force units to stay in an experiment.

When do we exclude cases? When do we