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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.

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。

【终译】假设乔正在参与 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。我们想要探究的因果效应，或者说治疗效果，就是指这两种潜在结果之间的差异。

{| class="wikitable"

{| class="wikitable"

!subject

!subject

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.

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。

【终译】 Yt(u) 表示如果乔服用了这种新药物之后对应的血压。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 的潜在结果或控制组的结果。Yc (u)若表示控制组，则在这种情况下，Yt (u)-Yc (u)就是表示乔不吃这种新药物时的血压，也就是服用这种新药物的因果效应。

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.

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.

Consider a larger sample of patients:

Consider a larger sample of patients:

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.

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。

【终译】每个实验对象的因果效应是不同的，从该表中，可知效应为负值，说明药物仅对乔，玛丽和鲍勃起作用。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.

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.