Can refill invitations increase repeat orders?
Study design
Randomly invite eligible shoppers who are due for a refill. Compare all invited and uninvited customers, including people who ignore the invitation.
Instrument and data fields
Record shopper ID, assignment, opt-in, refill purchase and days to reorder. Set a 30-day measurement window.
Simulated evidence
Invitation: 78 of 300 reordered and 120 opted in. Usual service: 63 of 300 reordered.
Check before drawing a conclusion
Write down the comparison you would make and the unit each row represents. Identify one explanation the study design cannot rule out, then describe how it would affect the decision.
Reveal the worked analysis
The observed invitation effect is 5 percentage points, from 21% to 26%. Base the economics on all eligible shoppers, not just the 120 opt-ins.
Opting in is a choice. Comparing opt-ins with other shoppers will generally mix selection with programme effects.