Teams often ask for “the lift number” before agreeing what an attach is. Is it any secondary line in the same order? Only lines from the recommended pair list? Only within 24 hours?
In our Bristol studies we lock three decisions early:
- Window — from impression to eligible order time.
- Eligible lines — category rules and price floors.
- Exclusions — gifts, replacements, and staff orders.
Without those, control and exposed groups are not comparable. A short definition memo saves a week of chart debate later. If you are scoping a lift study, bring your current attach definition to the discovery call — even if it is imperfect.