A group of people whose characteristics may be measured against those of a treatment group (intervention group); comparison group members have characteristics and demographics similar to those of the treatment (intervention) group, but members of the comparison group receive no intervention (or a different intervention).
Random assignment — making a comparison group as similar as possible to the intervention group, to rule out external influences; randomly allocating individuals to either the intervention group or the control group.
Controls in a randomised control trial (RCT) are people in a comparison group. They receive the usual treatment (or a placebo) while the experimental group receive the treatment being tested. (CASP)
EMCDDA