Open Access Research article

SYRCLE’s risk of bias tool for animal studies

Carlijn R Hooijmans1*, Maroeska M Rovers2, Rob BM de Vries1, Marlies Leenaars1, Merel Ritskes-Hoitinga1 and Miranda W Langendam3

Author Affiliations

1 SYRCLE at Central Animal Laboratory, Radboud University Medical Center, Nijmegen, the Netherlands

2 Centre of Evidence-based Surgery, Radboud University Medical Center, Nijmegen, the Netherlands

3 Dutch Cochrane Centre, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands

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BMC Medical Research Methodology 2014, 14:43  doi:10.1186/1471-2288-14-43

Published: 26 March 2014



Systematic Reviews (SRs) of experimental animal studies are not yet common practice, but awareness of the merits of conducting such SRs is steadily increasing. As animal intervention studies differ from randomized clinical trials (RCT) in many aspects, the methodology for SRs of clinical trials needs to be adapted and optimized for animal intervention studies. The Cochrane Collaboration developed a Risk of Bias (RoB) tool to establish consistency and avoid discrepancies in assessing the methodological quality of RCTs. A similar initiative is warranted in the field of animal experimentation.


We provide an RoB tool for animal intervention studies (SYRCLE’s RoB tool). This tool is based on the Cochrane RoB tool and has been adjusted for aspects of bias that play a specific role in animal intervention studies. To enhance transparency and applicability, we formulated signalling questions to facilitate judgment.


The resulting RoB tool for animal studies contains 10 entries. These entries are related to selection bias, performance bias, detection bias, attrition bias, reporting bias and other biases. Half these items are in agreement with the items in the Cochrane RoB tool. Most of the variations between the two tools are due to differences in design between RCTs and animal studies. Shortcomings in, or unfamiliarity with, specific aspects of experimental design of animal studies compared to clinical studies also play a role.


SYRCLE’s RoB tool is an adapted version of the Cochrane RoB tool. Widespread adoption and implementation of this tool will facilitate and improve critical appraisal of evidence from animal studies. This may subsequently enhance the efficiency of translating animal research into clinical practice and increase awareness of the necessity of improving the methodological quality of animal studies.

Risk of bias; Methodological quality; Animal studies; Systematic reviews; Tool; Translational research