Measure Campaign Lift with Control

Scenario

You work on a growth team running a campaign to drive users to complete a key activation step in an IT management product. The campaign will reach only part of the eligible audience, and stakeholders want to know whether any observed lift is truly caused by the campaign rather than by underlying user differences or timing.

Question

How would you use a control group to measure the impact of the campaign? Walk through how you would set up the experiment, define success, and decide whether the campaign worked.