A control group is isolated from the main experiment.

• It’s a group included with the experiment but are still partialy separated from the experiment.
• It’s a group included with the experiment.
• It’s a group separated from the rest of the experiment.
• It’s a group separated from the rest of the experiment but are still included in the test.

The correct answer is: It’s a group separated from the rest of the experiment.

Explanation: The control group is distinct, set apart from the core experiment. It includes existing campaigns that are comparable within an account, receiving half the traffic. It’s worth noting that for these advertisers, Performance Max traffic is either suppressed or stands at zero. Google’s approach involves leveraging both control and treatment groups to test incrementality, shunning retrospective comparisons. This methodology ensures precise measurement of ad efficacy, particularly when assessing key indicators such as online purchases or in-store sales through geo-based experiments.

Read more here: https://support.google.com/google-ads/answer/12997711