"ARM: Any of the treatment groups in a randomized trial. Most randomized trials have two "arms," but some have three "arms," or even more"
"CONTROL GROUP: The standard by which experimental observations are evaluated. In many clinical trials, one group of patients will be given an experimental drug or treatment, while the control group is given either a standard treatment for the illness or a placebo"http://clinicaltrials.gov/ct2/info/glossary
Experimental: An arm or group in which an experimental drug or regimen is being administered. This will be used when the trial specifies that one arm is a control arm and the other is experimental, or when the other arm is a placebo arm. In cases where patients are not randomized but assigned to groups according to certain characteristics (e.g., risk characteristics, age, diagnosis), use "experimental" for all groups/strata because they are not being compared.Active comparator
: An arm or group in which active drugs are given. This will include arms that are mixing active drugs and placebos. This will be used when the term "control arm" is specified in the protocol and when another arm is designated as the experimental arm. There can be more than one active comparator arm.Placebo comparator
: An arm or group in which ONLY a placebo is given.Sham comparator
: An arm or group in which ONLY a mock therapy that is not a drug is administered.
No intervention: An observational arm or group.
Other: An arm or group which does not fall into any of the above"http://www.cancer.gov/clinicaltrials/conducti...