在实际工作中，人们在采用回归模型解释因果变量间的相关关系时，经常会遇到自变量之间存在幂乘关系的情况。
In practical work, it is frequent that there is power relation among independent variables when the correlation between dependent variable and independent variables is explained by regression model.
这给人深刻印象的做法排除了因果变量，斯坦福大学的诺阿-古德曼说：“他们实际上自行设计了一个实验以获取他们想要的信息。”
That showed an impressive determination to isolate the causal variables, says Stanford’s Noah Goodman: “They actually designed an experiment to get the information they wanted.”
否则，统计学家表示只有进行严格的临床试验，对比一个控制组、一个测试组以及一个变量，才能真正证明因果关系。
Otherwise, statisticians say only strict clinical trials with a control group and a test group and one variable can truly prove a cause-and-effect association.
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