A factual outcome is the response actually observed after a unit receives, or does not receive, a treatment. For patient i, Y(i) is observable, while Y₀(i) and Y₁(i) describe outcomes under both possible assignments and only one is seen. If T(i)=1, Y(i)=Y₁(i); otherwise, Y(i)=Y₀(i). section 10.1.1
The factual outcome anchors causal comparisons: the unobserved result under the alternative assignment is the counterfactual outcome. In time-based designs, the observed series follows the untreated potential outcome before the event and the treated potential outcome afterward. section 10.1.1 section 11.2.2
Patient recovery table
Holden receives treatment and recovers, so T(i)=1 and Y(i)=1; the factual outcome is recovery, while the untreated potential outcome remains unavailable in ordinary observed data. Table 10.1 compares this pattern with patients who do not recover or receive no treatment. section 10.1.1
Table 10.1 Hypothetical example of POs with assignment (T(i)) and observed recovery (Y(i))
|
Name
|
i
|
Y
0(
i)
|
Y
1(
i)
|
T(
i)
|
Y(
i)
|
|---|---|---|---|---|---|
|
Drummer
|
1
|
0
|
0
|
1
|
0
|
|
Burton
|
2
|
1
|
0
|
1
|
0
|
|
Holden
|
3
|
0
|
1
|
1
|
1
|
|
Avasarala
|
4
|
1
|
1
|
0
|
1
|
Compare treatment assignment, both potential outcomes, and the single factual outcome observed for each patient. section 10.1.1
