Assessment of the risk of bias is an essential component of any systematic review. This is true for both nonrandomized studies and randomized trials, which are the main study designs of systematic reviews. The Risk of Bias Assessment Tool for Nonrandomized Studies (RoBANS) was developed in 2013 and has gained wide usage as a risk-of-bias assessment tool for nonrandomized studies. Four risk-of-bias assessment experts revised it by reviewing existing assessment tools and user surveys. The main modifications included additional domains of selection and detection bias susceptible to nonrandomized studies of interventions, a more detailed consideration of the comparability of participants, and more reliable and valid outcome measurements. A psychometric assessment of the revised RoBANS (RoBANS 2) revealed acceptable inter-rater reliability (weighted kappa, 0.25 to 0.49) and construct validity in which intervention effects of studies with an unclear or high risk of bias were overestimated. The RoBANS 2 has acceptable feasibility, fair-to-moderate reliability, and construct validity. It provides a comprehensive framework for allowing authors to assess and understand the plausible risk of bias in nonrandomized studies of interventions.
Keywords: Bias; Nonrandomized Studies; Risk Assessment; Systematic Review.