Why It Matters
Students live in classrooms, classrooms in universities. If I ignore this nesting, I treat meaningful context as 'error'.
What To Learn
- ICC (Intraclass Correlation Coefficient): How much of the variance is due to the 'group'?
- Grand-mean vs. Group-mean centering: Interpreting effects within-group vs. between-group.
- Sample Size requirements: 30 groups of 30 is better than 10 groups of 100.