Randomized Controlled Trials (RCTs) often adjust for baseline covariates in order to increase power. This technical note provides a short derivation of a simple rule of thumb for approximating the ratio of the power of an adjusted analysis to that of an unadjusted analysis. Specifically, if the unadjusted analysis is powered to approximately 80\%, then the ratio of the power of the adjusted analysis to the power of the unadjusted analysis is approximately $1 + \frac{1}{2} R^2$, where $R$ is the correlation between the baseline covariate and the outcome.

翻译：随机对照试验（RCT）常通过调整基线协变量来提高统计效能。本技术注释简要推导了一个简单经验法则，用于近似估计经调整分析与未调整分析统计效能的比值。具体而言，若未调整分析的统计效能约为80%，则经调整分析统计效能与未调整分析统计效能之比近似为 $1 + \frac{1}{2} R^2$，其中 $R$ 为基线协变量与结局之间的相关系数。