01644nas a2200325   4500000000100000000000100001008003900002260001600041653002100057653002600078653003400104653001700138653002000155653003400175653001200209653002800221100002100249700002000270700002000290700003300310700002300343700001800366700001900384245010800403856008200511300001300593490000700606520069100613022001401304       0                             d  cJan 4, 201610aCancer treatment10aCancers and neoplasms10aDrug research and development10aMetaanalysis10aResearch errors10aResearch reporting guidelines10aRodents10aSimulation and modeling1 aConstance Holman1 aSophie K. Piper1 aUlrike Grittner1 aAndreas Antonios Diamantaras1 aJonathan Kimmelman1 aBob Siegerink1 aUlrich Dirnagl00aWhere Have All the Rodents Gone? The Effects of Attrition in Experimental Research on Cancer and Stroke  uhttps://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002331  ae10023310 v143 aGiven 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.  a1545-7885