RoB 2 vs. ROBINS-I vs. Newcastle-Ottawa Scale

Using the wrong risk-of-bias tool for your study design is a common, avoidable error — each tool is built around the specific biases that threaten a particular type of study.

RoB 2

For randomized controlled trials. Assesses bias across five domains: the randomization process, deviations from intended interventions, missing outcome data, outcome measurement, and selection of the reported result. See our full RoB 2 guide.

ROBINS-I

For non-randomized studies of interventions (e.g., comparing treated vs. untreated groups without randomization). Assesses confounding, selection bias, and other domains specific to the absence of randomization — generally requires more judgment and is more time-intensive to apply than RoB 2.

Newcastle-Ottawa Scale (NOS)

For cohort and case-control studies. Uses a star-rating system across three domains: selection, comparability, and outcome/exposure. Simpler to apply than ROBINS-I, though criticized by some methodologists for less granular guidance than newer tools.

Other tools worth knowing

• QUADAS-2 — for diagnostic accuracy studies.
• AMSTAR-2 — for appraising systematic reviews themselves (used in umbrella reviews).
• JBI Critical Appraisal Tools — a family of checklists covering multiple study designs, including qualitative research.

Quick decision guide

• Randomized trial → RoB 2
• Non-randomized intervention study → ROBINS-I
• Cohort or case-control study → Newcastle-Ottawa Scale
• Diagnostic accuracy study → QUADAS-2