Institute of Medical Biometry and Medical Informatics, University of Freiburg, Freiburg, Germany.
J Clin Epidemiol. 2012 Nov;65(11):1171-80. doi: 10.1016/j.jclinepi.2012.04.008.
To display and discuss the reasons and consequences of length and time-dependent bias. They might occur in presence of a time-dependent study entry or a time-dependent exposure which might change from unexposed to exposed.
Recalling the popular study of Oscar nominees and using a real-data example from hospital epidemiology, we give innovative and easy-to-understand graphical presentations of how these biases corrupt the analyses via distorted time-at-risk. Cumulative hazard plots and Cox proportional hazards models were used. We are building bridges to medical disciplines such as critical care medicine, hepatology, pharmaco-epidemiology, transplantation medicine, neurology, gynecology and cardiology.
In presence of time-dependent bias, the hazard ratio (comparing exposed with unexposed) is artificially underestimated. The length bias leads to an artificial underestimation of the overall hazard. When both biases coexist it can lead to different directions of biased hazard ratios.
Since length and time-dependent bias might occur in several medical disciplines, we conclude that understanding and awareness are the best prevention of survival bias.
展示并讨论与长度和时间依赖性偏倚有关的原因和后果。这些偏倚可能出现在有时间依赖性的研究入组或时间依赖性暴露的情况下，此时暴露状态可能会从无暴露变为有暴露。
我们回顾了奥斯卡提名者的热门研究，并使用医院流行病学中的真实数据示例，通过风险暴露时间的扭曲，以创新且易于理解的图形方式展示了这些偏倚如何通过分析结果。我们使用了累积风险图和 Cox 比例风险模型。我们正在为诸如重症医学、肝脏病学、药物流行病学、移植医学、神经病学、妇科学和心脏病学等医学学科架起桥梁。
在存在时间依赖性偏倚的情况下，风险比（比较暴露组与无暴露组）会被人为低估。长度偏倚会导致整体风险的人为低估。当这两种偏倚同时存在时，可能会导致风险比出现不同的偏倚方向。
由于长度和时间依赖性偏倚可能出现在多个医学学科中，我们得出结论，理解和意识是预防生存偏倚的最佳方法。
