How likely a study's design flaws are to have distorted its result.
Risk of Bias is a structured judgement of how likely flaws in a study's design or conduct — such as poor randomisation, lack of blinding, or selective reporting — are to have distorted its findings. Reviewers use standard tools (for example RoB 2 or ROBINS-I) to rate it. A study can report a striking result yet carry a high risk of bias, which should temper how much weight it is given.