Business Context

FinFlow, a personal finance app with 2.4M monthly active users, launched a referral program 8 weeks ago offering both the inviter and invitee a $10 reward after the invitee links a bank account and completes their first transaction. Leadership wants to know whether the program is actually effective or just adding incentive cost without improving durable growth.

Metric Scenario

Before launch, FinFlow averaged 48,000 new signups per week, 62% bank-link conversion, 41% first-transaction conversion within 14 days, and 8-week retention of 29% for new users. In the 8 weeks after launch, weekly signups increased to 61,000. Of those, 18,000 per week came through referral invites. Referred users showed 78% bank-link conversion, 56% first-transaction conversion within 14 days, and projected 8-week retention of 35%. The company paid $1.12M in referral rewards during the period. Paid acquisition spend stayed flat, but organic signups fell from 31,000 to 26,000 per week.

Requirements

1. Define the primary KPI you would use to assess the referral program's effectiveness and explain why.
2. Separate incremental impact from cannibalization or channel shifting.
3. Identify the leading and lagging indicators you would monitor in the first 30, 60, and 90 days.
4. Decompose performance by user quality, funnel conversion, retention, and cost efficiency.
5. Recommend whether FinFlow should scale, modify, or pause the program.

Data Available

• referral_invites: inviter_id, invitee_id, invite_sent_at, invite_accepted_at, reward_paid_at
• user_signup_attribution: user_id, signup_date, acquisition_channel, campaign_id
• onboarding_funnel: user_id, bank_linked_at, first_transaction_at
• weekly_retention: user_id, signup_week, retained_week_1_to_week_8
• marketing_spend: week, channel, spend, rewarded_users, incentive_cost