A control group is the set of participants who do not receive the change being tested, so researchers have a baseline to compare against. Without one, any improvement could come from timing, mood, the placebo effect, or plain chance.<\/p>\n\n\n\n
That comparison is why control groups sit at the heart of drug trials, A\/B tests, and survey experiments. A reworded question, a redesigned email, or a wellness program only proves its worth when a similar group went without it.<\/p>\n\n\n\n
In this guide, you’ll learn what a control group is, the seven main types, how to size and design one, and how to read the results.<\/p>\n\n\n\n\n\n
A control group is a set of participants in an experiment who do not receive the treatment, change, or intervention being tested. Researchers compare their results with those of the experimental group to see what the change actually did.<\/p>\n\n\n\n
Think of it as the “what would have happened anyway” group. If both groups improve by the same amount, the change did nothing. If only the experimental group improves, the change likely worked.<\/p>\n\n\n\n
The idea reaches far beyond medicine. A survey researcher might show the control group the original question and the experimental group a reworded one. A marketer might send the usual email to the control group and a new design to everyone else. In each case, the only planned difference between the groups is the change itself. That is the core logic of experimental research<\/a>.<\/p>\n\n\n\n A valid control group needs three things:<\/p>\n\n\n\n The control group does not get the change, and the experimental group does. Everything else about the two groups should match, so any gap in results points back to the change.<\/p>\n\n\n\n\n
What is the difference between a control group and an experimental group?<\/strong><\/h2>\n\n\n\n