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do you need tiers
Define the rule, cost, member promise, and operational control before launch. Use observed behaviour for thresholds and test the full liability case.
The design decision for do you need tiers is economic and operational. Define the behaviour, cost, ledger event, and member promise before launch.
## The mechanism useful design has a clear trigger, measurable threshold, redemption or control path, and owner. Keep qualification, liability, reversals, consent, and expiry as separate rules.
## Worked example is illustrative arithmetic. A member earns 2 points per dollar on 400 dollars of spend, creating 800 points. At 1 cent per point, the balance represents 8 dollars. A change to 3 points creates 1,200 points worth 12 dollars, increasing visible value by 4 dollars.
## Do it the rule in one sentence. Test the qualifying event, member explanation, operator cost, reversal, and exit condition. Compare the result with a holdout or simpler alternative.
## Common mistakes
- Confusing activity with changed behaviour. Measure the counterfactual. - Treating face value as cost. Use operator cost. - Hiding the rule. Publish thresholds and notices. - Relying on breakage. Test full redemption.