All observational studies are liable to confounding and Levin’s formula becomes useless in practice for unbiasedly estimating PAF. With respect to causal interpretation of PAF in public health setting, unbiased estimation of PAF requires several assumptions which are ignored in practice. We recommend using Miettinen PAF formula with careful consideration about possibility of bias in study design and analysis.

中文翻译：

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从全球角度看燃煤电厂和肺癌负担中人口归因分数（PAF）计算不正确的问题

所有观察性研究都容易混淆，在实际中无偏估计PAF时，Levin公式变得毫无用处。关于公共卫生环境中PAF的因果解释，对PAF的无偏估计需要几个假设，而这些假设在实践中会被忽略。我们建议使用Miettinen PAF公式，并仔细考虑研究设计和分析中可能存在的偏倚。