Definitions for "Blind study"
one in which the subject or the investigator (or both) are unaware of what trial product a subject is taking. See also double-blind study, single-blind study, triple-blind study
Because human psychology plays a big part in how we respond to things, blinding may be employed to ensure that subjects in an experiment do not know which of the treatments they are receiving. This is used to combat bias. For example, in a clinical trial people's beliefs could affect the outcome; thus non-drug treatment may appear to be more effective on advocates of alternative medicine. See also bias, blinded evaluation, double blind, single blind.
A double blind clinical study is one in which neither patient nor the investigator knows which drug is being administered during the study. In a single blind study the investigator but not the patient will know which drug is being taken.