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无编辑摘要
=== Potential outcomes ===
== 定义 ==
潜在结果：给定一个单元，和一系列动作，我们把一个“动作-单元”确定为一个潜在结果。“潜在(potential)”这个词表达的意思是我们并不总是能在现实中观察到这个结果(outcome)，但原则上它们可能发生。
== 样例介绍 ==
Suppose that Joe is participating in an FDA test for a new hypertension drug. If we were omniscient, we would know the outcomes for Joe under both treatment (the new drug) and control (either no treatment or the current standard treatment). The causal effect, or treatment effect, is the difference between these two potential outcomes.
【终译】假设 Joe 正在参与 FDA 对一种新的高血压药物的测试。如果我们是无所不知的，我们就会知道乔在治疗组和控制组下的结果。因果效应，或治疗效果，是指这两种潜在结果之间的差异。
{| class="wikitable"
!subject
!Yt(u)
!Yc (u)
!Yt (u)-Yc (u）
|-
!Joe
|130
|135
|−5
|}
Yt(u) is Joe's blood pressure if he takes the new pill. In general, this notation expresses the potential outcome which results from a treatment, ''t'', on a unit, ''u''. Similarly, Yc(u) is the effect of a different treatment, ''c'' or control, on a unit, ''u''. In this case, Yt(u) - Yc(u) is Joe's blood pressure if he doesn't take the pill. is the causal effect of taking the new drug.
【终译】 Yt(u) 表示如果乔服用了这种新药丸之后对应的血压。一般来说，这个符号表示一个单位 u 上的治疗结果 t 的潜在结果。类似地，Yc (u)是一个单位 u 上的不同治疗效果 c 或控制。在这种情况下，Yt (u)-Yc (u)是乔不吃这种新药时的血压，也就是服用这种新药的因果效应。
From this table we only know the causal effect on Joe. Everyone else in the study might have an increase in blood pressure if they take the pill. However, regardless of what the causal effect is for the other subjects, the causal effect for Joe is lower blood pressure, relative to what his blood pressure would have been if he had not taken the pill.
【终译】从这个表格中我们只知道对乔的因果关系。研究中的其他人如果服用新药，血压可能会升高。然而，不管其他受试者的因果关系如何，对于 Joe 来说，因果关系是血压降低，相对于如果他没有服用新药的话，他的血压会降低。
Consider a larger sample of patients:
【终译】考虑更为大量的病患样本
{| class="wikitable"
!subject
!Yt(u)
!Yc (u)
!Yt (u)-Yc (u）
|-
!Joe
|130
|135
|−5
|-
!Mary
|140
|150
|−10
|-
!Sally
|135
|125
|10
|-
!Bob
|135
|150
|−15
|}
The causal effect is different for every subject, but the drug ''works'' for Joe, Mary and Bob because the causal effect is negative. Their blood pressure is lower with the drug than it would have been if each did not take the drug. For Sally, on the other hand, the drug causes an increase in blood pressure.
【终译】每个实验对象的因果效应是不同的，但药物仅对乔，玛丽和鲍勃起作用，因为因果效应是负面的。他们服用这种药物后的血压比没有服用这种药物时的血压要低。另一方面，对于 Sally 来说，这种药物会导致血压升高。
In order for a potential outcome to make sense, it must be possible, at least ''a priori''. For example, if there is no way for Joe, under any circumstance, to obtain the new drug, then is impossible for him. It can never happen. And if can never be observed, even in theory, then the causal effect of treatment on Joe's blood pressure is not defined.
【终译】为了让一个潜在的结果有意义，它必须是可能的，至少是先验的。例如，如果乔在任何情况下都没有办法获得新药，那么他就不可能获得。这永远不可能发生。如果不能观察到，即使在理论上，那么治疗对乔的血压的因果效应也不能确定。