诀窍在于找到一种“工具性可变因素”，它能在统计分析中代替某种可变因素，但它显然与其他可变因素无关。
The trick is to find an “instrumental variable” which can act as a proxy for one variable in a statistical analysis, but which is clearly unrelated to the others.
诀窍在于找到一种“工具性可变因素”，它能在统计分析中代替某种可变因素，但它显然与其他可变因素无关。
The trick is to find an “instrumental variable” which can act as a proxy for one variable in a statistical analysis, but which is clearly unrelated to the others.
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