Performance bias may occur if participants in a study (the people receiving, and delivering the treatments being compared) are aware of which participants received which treatments. For example, patients in a treatment comparison group who know that they have been allocated to not receive a new treatment that is being tested may be more likely to use other forms of care.
Patients in a treatment comparison group who know that they are receiving the new treatment being tested may be more likely to experience placebo effects.
Healthcare providers may treat patients differently according to which group they are in.
Blinding of participants (e.g. patients and healthcare providers) in a study is used to reduce the risk of this bias, and often involves the use of placebos.
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