You are a senior product analyst on a consumer fintech app that offers pay-over-time purchases through its app and merchant integrations. A new personalized prequalification entry point was launched on the Affirm app home feed 6 weeks ago, and weekly prequalification starts increased from 420,000 to 560,000 (+33%) while completed purchases only rose from 118,000 to 123,000 (+4%). At the same time, starts from search and merchant deep links fell 18%, and repeat-user purchase rate stayed flat at 21%. Product leadership wants to know whether the feature is generating incremental growth or mostly cannibalizing existing discovery paths before expanding it to all users.
How would you evaluate whether this feature is creating true incremental growth versus shifting behavior from existing surfaces, and what metrics would you use to make that call?