When comparing mammography-screening participants and non-participants, estimates of reduction in breast-cancer mortality may be biased by poor baseline comparability. We used negative controls to detect uncontrolled confounding.

中文翻译：

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阴性对照用于检测比较参与者和非参与者的乳房 X 线摄影筛查观察性研究中不受控制的混杂因素。


当比较乳房X光检查筛查参与者和非参与者时，乳腺癌死亡率降低的估计可能会因基线可比性较差而产生偏差。我们使用阴性对照来检测不受控制的混杂因素。