Novelty effect
The novelty effect is a temporary response lift caused by a change being new rather than better. It decays as customers habituate, so short tests systematically overstate the durable impact of visible interface, creative or messaging changes.
Why it matters for ARPU
Growth programmes that ship on week-one results accumulate wins that quietly disappear, which is a common reason reported gains never show up in annual ARPU.
Related terms
A/B testAn A/B test randomly assigns customers to two or more variants and compares a pre-declared metric between them.IncrementalityIncrementality is the portion of an outcome that would not have happened without the action.Cohort analysisCohort analysis groups customers by a shared starting characteristic, usually acquisition month, and follows each group over time.Guardrail metricA guardrail metric is a measure an experiment must not damage even if the primary metric improves: unsubscribe rate, complaint volume, margin, support contacts, app uninstalls.