Correction of Survival Bias in a Study About Increased Mortality of Heads of Government

A recent study reported increased mortality of heads in government. To avoid the time-dependent bias (also known as immortal-time bias), survival from <i>last</i> election was compared between election winners and runners-up. We claim that this data manipulation results in bias due to conditioning on future events; survival should be compared from <i>first</i> election as well as winning should be considered as a time-dependent covariate. We collected the missing life-time periods and redesigned the study to display this bias using Lexis diagrams and multistate methodology. We found that the bias that we termed the healthy candidate bias was even more severe than the time-dependent bias.

近期一项研究报道了政府首脑死亡率升高的现象。为规避时间依赖性偏倚（time-dependent bias，亦称永存时间偏倚（immortal-time bias）），该研究以末次选举为时间起点，对比了选举获胜者与落选候选人的生存状况。我们认为，该数据处理方式因对未来事件进行条件性设定而引入偏倚；生存分析的起点应选取首次选举，同时应将当选视作时间依赖性协变量。我们收集了缺失的生命周期数据，并重新设计了研究方案，借助莱克西斯图（Lexis diagrams）与多状态模型方法展示该偏倚。研究发现，我们命名为健康候选人偏倚的此类偏倚，其严重程度甚至超过了时间依赖性偏倚。