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Methodology May 15, 2026 7 min read

RoB 2, ROBINS-I, NOS, QUADAS-2: Which Risk of Bias Tool to Use?

Six validated tools are available. This guide maps each tool to the study design it covers.

V
Verflux Team
Published May 15, 2026

Why Risk of Bias Assessment Matters

Risk of bias assessment is a mandatory component of systematic reviews. It evaluates whether the design and conduct of individual studies introduce systematic errors that could distort the true effect. Cochrane Handbook and PRISMA 2020 both require it.

Cochrane RoB 2 — For Randomised Controlled Trials

The revised Cochrane risk of bias tool (RoB 2) assesses bias across five domains: randomisation process, deviations from intended interventions, missing outcome data, measurement of the outcome, and selection of the reported result. Each domain is rated Low, Some concerns, or High.

ROBINS-I — For Non-Randomised Studies of Interventions

ROBINS-I covers seven domains: confounding, selection of participants, classification of interventions, deviations from interventions, missing data, measurement of outcomes, and selection of reported results. Ratings: Low, Moderate, Serious, Critical, or No information.

Newcastle-Ottawa Scale (NOS) — For Observational Studies

The NOS uses a star system across three domains: selection (4 stars), comparability (2 stars), and outcome/exposure (3 stars). Scores ≥7 are generally considered low risk. Available for cohort and case-control designs.

QUADAS-2 — For Diagnostic Accuracy Studies

QUADAS-2 assesses four domains: patient selection, index test, reference standard, and flow and timing. Each is rated for risk of bias and applicability concerns.

AXIS — For Cross-Sectional Studies

The Appraisal tool for Cross-Sectional Studies (AXIS) uses 20 items covering study design, sampling, data collection, statistical analysis, and reporting. Supported in Verflux.

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