为什么存在这样的差别呢？
这就应该解释了为什么较富裕国家的平均幸福度不会显得比较贫穷国家的高，因为在较富裕国家同龄人之间的富裕水平也有差别。这样拿收入做参考的假设只是扯淡。
This was supposed to be the reason why average happiness did not appear to be higher in richer than poorer countries since one's peers also have higher incomes in richer countries.
这种模型表明了我们知识的一种缺乏，这都是为什么真正的、显著的效应的差别要通过这样一个随机模型。
The model represents our lack of knowledge about why real, or apparent, treatment effects differ by considering the differences as if they were random.
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