Where Have All the Rodents Gone? The Effects of Attrition in Experimental Research on Cancer and Stroke

Given small sample sizes, loss of animals in preclinical experiments can dramatically alter results. However, effects of attrition on distortion of results are unknown. We used a simulation study to analyze the effects of random and biased attrition. As expected, random loss of samples decreased statistical power, but biased removal, including that of outliers, dramatically increased probability of false positive results. Next, we performed a meta-analysis of animal reporting and attrition in stroke and cancer. Most papers did not adequately report attrition, and extrapolating from the results of the simulation data, we suggest that their effect sizes were likely overestimated.在样本量较小的临床前实验（preclinical experiments）中，动物脱落会显著改变实验结果。然而，目前学界尚未明确脱落情况对实验结果偏差的具体影响。本研究通过模拟实验，分析了随机脱落与偏倚性脱落对实验结果的作用效果。正如预期，样本随机脱落会降低统计功效（statistical power）；而包括异常值（outliers）剔除在内的偏倚性移除操作，则会显著提升假阳性结果的发生概率。随后，本研究针对脑卒中与癌症领域的动物实验报告及脱落情况开展了元分析（meta-analysis）。结果显示，绝大多数论文未对动物脱落情况进行充分报告；结合模拟实验结果外推可知，此类研究的效应量（effect sizes）很可能被高估了。