Instruments for assessing risk of bias and other methodological criteria of published animal studies: a systematic review

Environ Health Perspect. 2013 Sep;121(9):985-92. doi: 10.1289/ehp.1206389. Epub 2013 Jun 14.


Background: Results from animal toxicology studies are critical to evaluating the potential harm from exposure to environmental chemicals or the safety of drugs prior to human testing. However, there is significant debate about how to evaluate the methodology and potential biases of the animal studies. There is no agreed-upon approach, and a systematic evaluation of current best practices is lacking.

Objective: We performed a systematic review to identify and evaluate instruments for assessing the risk of bias and/or other methodological criteria of animal studies.

Method: We searched Medline (January 1966-November 2011) to identify all relevant articles. We extracted data on risk of bias criteria (e.g., randomization, blinding, allocation concealment) and other study design features included in each assessment instrument.

Discussion: Thirty distinct instruments were identified, with the total number of assessed risk of bias, methodological, and/or reporting criteria ranging from 2 to 25. The most common criteria assessed were randomization (25/30, 83%), investigator blinding (23/30, 77%), and sample size calculation (18/30, 60%). In general, authors failed to empirically justify why these or other criteria were included. Nearly all (28/30, 93%) of the instruments have not been rigorously tested for validity or reliability.

Conclusion: Our review highlights a number of risk of bias assessment criteria that have been empirically tested for animal research, including randomization, concealment of allocation, blinding, and accounting for all animals. In addition, there is a need for empirically testing additional methodological criteria and assessing the validity and reliability of a standard risk of bias assessment instrument.

Publication types

  • Research Support, N.I.H., Extramural
  • Review
  • Systematic Review

MeSH terms

  • Animals
  • Bias*
  • Double-Blind Method
  • Random Allocation
  • Research Design / standards*
  • Risk Assessment / methods*
  • Sample Size
  • Toxicity Tests / methods
  • Toxicity Tests / standards*