Business Context

Affirm is testing a redesigned checkout entry experience on the Affirm checkout surface to increase application-start-to-checkout conversion. Product wants to ship only if the change improves top-of-funnel conversion without degrading downstream quality, measured by 30-day repayment delinquency among originated loans.

Problem Statement

Design and analyze the experiment using the data below. Determine whether the treatment should be rolled out if it increases checkout conversion but must not materially worsen downstream credit quality.

Given Data

The experiment ran for 21 days with user-level randomization on eligible checkout sessions.

Additional test settings:

Requirements

1. Define the primary metric, guardrail metric, and the null/alternative hypotheses for both.
2. Test whether conversion improved using a two-proportion z-test.
3. Construct a 95% confidence interval for the conversion lift.
4. Test whether delinquency is non-inferior using the stated margin.
5. State the launch decision under the rule: ship only if conversion is significantly higher and delinquency is not worse than the margin.
6. Briefly comment on whether the sample size appears adequate for the planned conversion MDE.

Assumptions

• Randomization is valid and each eligible session appears once.
• Delinquency is evaluated only on originated loans.
• No major traffic-mix shift occurred during the 21-day window.
• Ignore multiple secondary metrics beyond the stated guardrail.