From Longman Business Dictionarycontrol groupconˈtrol group noun [countable]STATISTICS in a test, a group of people or things that you do not test and that you then compare with the group being tested. By using a control group, you can see if the results of your test are caused by the thing you are testing or are caused by chanceIt found that households buying the magazine spent 7% more a week on groceries than a control group.