control group conˈtrol 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 chance:
• It found that households buying the magazine spent 7% more a week on groceries than a control group.
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control group UK US noun [C] (also control) MARKETING
► a group of people who are used for comparing another group to in a test or experiment: »
The larger the control group sample is, the more reliable and repeatable the results of the promotion will be.
Financial and business terms. 2012.