A double-blind study or experiment compares two groups of people, one of which is being tested while the other is not. Neitherthe people doing the testing nor the members of the two groups know which group isbeing tested.
In a double-blind trial, there were definite improvements.
double-blind in British English
adjective
of or relating to an experiment to discover reactions to certain commodities, drugs, etc, in which neither the experimenters nor the subjects know the particulars of the test items during the experiments
Compare single-blind
double-blind in American English
(ˈdʌbəlˈblaɪnd)
US
adjective
designating or of a technique used to test objectively the effects of a drug, course of treatment, etc. in which neither the subjects nor the researchers know during the testing whois actually receiving the drug, treatment, etc. and who is not, as in an experiment involving a drug and a placebo