Shirley E A, Newnham P
Stat Med. 1984 Jan-Mar;3(1):85-91. doi: 10.1002/sim.4780030110.
The problem of when to include a covariate in the analysis of variance is considered in the special case of organ weight analysis in animal toxicology studies. The covariate is bodyweight prior to death, which may be subject to treatment effects. A simulation study is carried out to compare four rules for deciding whether or not to include the covariate. It is concluded that if there is background information which shows a linear relationship between variate and covariate it is advisable to adjust for the covariate, however weak the relationship may appear to be on the current set of data. Alternative procedures lead to unacceptably high Type I error rates.
在动物毒理学研究中器官重量分析的特殊情况下，考虑了在方差分析中何时纳入协变量的问题。协变量是死亡前的体重，其可能受到治疗效果的影响。开展了一项模拟研究，以比较用于决定是否纳入协变量的四条规则。得出的结论是，如果有背景信息表明变量与协变量之间存在线性关系，那么无论当前数据集上这种关系看起来多么微弱，对协变量进行调整都是可取的。其他程序会导致I型错误率高得令人无法接受。
