6. single blind and double blind trials

SummaryThe purpose of blind trials is to reduce observer bias (subjective interpretation of results and heterosuggestion) and patient bias (subjective interpretation of symptoms and autosuggestion) by concealing the identity of the treatment administered either from the patient, the physician (which entails examination of the patient by a "blind" observer), or from both.When the identity of the treatment is concealed from both patient and physician, the trial is termed "double-blind". The following conditions must be observed when performing a double-blind trial: •the drugs compared should be as indistinguishable as possible;•the code should be accessible in case of an emergency;•strict precautions should be taken to avoid leaks.Sometimes, an "open" (non-blind) study may provide for "blind" interpretation of results by a third person who remains unaware of treatment assignment. It is preferable to conduct an open trial rather than a false double blind trial in which the treatments have been made blatantly obvious by "leaks" or by their characteristic effects.