Table 1 Four subgroups defined in terms of counterfactuals by combinations of assignment and exposure
From: An introduction to instrumental variable assumptions, validation and estimation
| Z = 0 | ||
|---|---|---|
| X = 0 | X = 1 | |
| Z = 1 | ||
| X = 0 | Never takers | Defiers |
| X = 1 | Compliers | Always takers |