Evidence-appraisal glossary
Performance bias
Performance bias is systematic error from differences in the care or attention that comparison groups receive, apart from the intervention being tested. Blinding of participants and staff is the main defense against it.
Performance bias arises when knowing who is in which group changes behavior, for example clinicians giving extra co-treatments to one arm or participants altering their own habits. It is one of the domains that risk-of-bias tools assess in randomized trials. Note that failure to blind does not automatically prove performance bias occurred; it means the trial could not rule it out, which is why such trials are rated at higher risk.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.