DOUBLE-BLIND STUDY

clinical study in which neither organizers nor participants know which individuals belong to the test group or the control group (Medicine, Psychology)

The double blind method is an important part of the scientific method, used to prevent research outcomes from being 'influenced' by either the placebo effect or the observer bias. Blinded research is an important tool in many fields of research, from medicine, to psychology and the social sciences, to forensics.
See more at Wikipedia.org...

Noun
1. an experimental procedure in which neither the subjects of the experiment nor the persons administering the experiment know the critical aspects of the experiment; a double-blind procedure is used to guard against both experimenter bias and placebo effects
(synonym) double-blind procedure, double-blind experiment
(hypernym) experimental procedure

Any clinical experiment designed so that none of the participants (e.g., the subjects and those treating them) knows the identity of the treatment any subject is undergoing.