Your question is Conversion Lift or Noise. 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're reviewing an experiment on a signup flow and need to judge whether an observed conversion change reflects a real effect or normal variation. You want a principled way to separate signal from noise.
How would you decide whether a change in conversion rate is real or just noise?