干预

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查询

Queries

Queries are questions asked based on a specific model. They are generally answered via performing experiments (interventions). Interventions take the form of fixing the value of one variable in a model and observing the result. Mathematically, such queries take the form (from the example) where the do operator indicates that the experiment explicitly modified the price of toothpaste. Graphically, this blocks any causal factors that would otherwise affect that variable. Diagramatically, this erases all causal arrows pointing at the experimental variable.

More complex queries are possible, in which the do operator is applied (the value is fixed) to multiple variables.

【终译】

查询是基于特定模型提出的问题。他们通常通过进行实验(干预)来回答。干预措施的形式是固定一个模型中一个变量的值，并观察结果。在数学上，这样的查询采取的形式(来自示例)

实验操作者指出实验明确地调整了牙膏的价格。从图形上看，这阻止了任何原本会影响该变量的因果因素。从图表上看，这清除了所有指向实验变量的因果箭头。

可以进行更复杂的查询，其中将 do 运算符(值是固定的)应用于多个变量。

Do算子

Do calculus

The do calculus is the set of manipulations that are available to transform one expression into another, with the general goal of transforming expressions that contain the do operator into expressions that do not. Expressions that do not include the do operator can be estimated from observational data alone, without the need for an experimental intervention, which might be expensive, lengthy or even unethical (e.g., asking subjects to take up smoking). The set of rules is complete (it can be used to derive every true statement in this system). An algorithm can determine whether, for a given model, a solution is computable in polynomial time.

【终译】

Do 演算是一组可用于将一个表达式转换为另一个表达式的操作，其总体目标是将包含 do 操作符的表达式转换为不包含 do 操作符的表达式。不包括 do 操作者的表情可以单独从观察数据中估计出来，不需要实验干预，这可能是昂贵的，冗长的，甚至是不道德的(例如，要求受试者吸烟)。规则集是完整的(可以用它来派生该系统中的每个真实语句)。算法可以确定，对于给定的模型，一个解是否在多项式时间内可计算。

规则

Rules

The calculus includes three rules for the transformation of conditional probability expressions involving the do operator.

【终译】

这个表达式包含了三个涉及 do 运算符的条件概率表达式转换规则。

Rule 1

Rule 1 permits the addition or deletion of observations.:

in the case that the variable set Z blocks all paths from W to Y and all arrows leading into X have been deleted.

【终译】

规则1 允许对观察变量进行增加或者删除

在这个例子中，变量集合Z阻断了所有从W到Y的路径，并且所有指向X的箭头被删除

Rule 2

Rule 2 permits the replacement of an intervention with an observation or vice versa.:

in the case that Z satisfies the back-door criterion.

【终译】

规则2允许用观察来替代干预，或者反之亦然

在这个例子中，变量集合Z满足后门标准

Rule 3

Rule 3 permits the deletion or addition of interventions.:

in the case where no causal paths connect X and Y.

【终译】

规则3允许对干预进行增加或者删除

在这个例子中，X和Y之间没有因果路径相连接

拓展

The rules do not imply that any query can have its do operators removed. In those cases, it may be possible to substitute a variable that is subject to manipulation (e.g., diet) in place of one that is not (e.g., blood cholesterol), which can then be transformed to remove the do. Example:

【终译】

这些规则并不意味着可以删除任何查询的 do 运算符。在这些情况下，可以用一个受操纵的变量(例如饮食)来代替一个不受操纵的变量(例如血液胆固醇) ，然后这个变量可以被转化去除胆固醇。例子: