Your question is Incrementality of a Growth Channel. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You are analyzing a paid growth channel and the team wants to know whether it creates new conversions or mainly takes credit for users who would have converted anyway. The channel was launched in one set of markets while similar markets stayed off, and you have pre and post conversion data.
How would you evaluate whether a growth channel is actually incremental versus just capturing existing demand?