Blinding: A procedure used in clinical trials to get rid of the possible bias which might be introduced if the patient and/or the doctor knew which treatment the patient is receiving. If neither the patient nor the doctor are aware of which treatment has been given the trial is known as double-blind. If only one out of the patient or doctor is unaware of the treatment, then the trial is called single-blind. Clinical trials should use maximum degree of blindness which is possible, even though in some areas, for instance, surgery, it is often not possible for an investigation to be double-blind.