<Ul> <Li> Randomized: Each study subject is randomly assigned to receive either the study treatment or a placebo . </Li> <Li> Blind: The subjects involved in the study do not know which study treatment they receive . If the study is double - blind, the researchers also do not know which treatment a subject receives . This intent is to prevent researchers from treating the two groups differently . A form of double - blind study called a "double - dummy" design allows additional insurance against bias . In this kind of study, all patients are given both placebo and active doses in alternating periods . </Li> <Li> Placebo - controlled: The use of a placebo (fake treatment) allows the researchers to isolate the effect of the study treatment from the placebo effect . </Li> </Ul> <Li> Randomized: Each study subject is randomly assigned to receive either the study treatment or a placebo . </Li> <Li> Blind: The subjects involved in the study do not know which study treatment they receive . If the study is double - blind, the researchers also do not know which treatment a subject receives . This intent is to prevent researchers from treating the two groups differently . A form of double - blind study called a "double - dummy" design allows additional insurance against bias . In this kind of study, all patients are given both placebo and active doses in alternating periods . </Li> <Li> Placebo - controlled: The use of a placebo (fake treatment) allows the researchers to isolate the effect of the study treatment from the placebo effect . </Li>

He purpose of making a clinical study double-blind is to