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

PLoS Biol. 2016 Jan 4;14(1):e1002331. doi: 10.1371/journal.pbio.1002331. eCollection 2016 Jan.


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.

Publication types

  • Meta-Analysis
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animal Experimentation*
  • Animals
  • Computer Simulation
  • Neoplasms
  • Rodentia
  • Sample Size*
  • Stroke

Grant support

UG was supported by Charité and the Steinbeis Foundation. UD and BS would like to acknowledge the financial support of the German Federal Ministry of Education and Research (BMBF 01 EO 08 01). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.