Evidence Half-Life Ledger

Every research finding an agency hands a client carries an expiry date, and the Evidence Half-Life Ledger is a way of assigning one at the moment the finding is created. Self-reported survey answers decay fastest because the market, the competitor set, and the respondent's own situation move underneath them; behavioral observations decay slower but still drift. The framework asks three questions per data point: what kind of evidence is it, how volatile is the thing it describes, and what event should force a refresh. A pricing perception captured in a Typeform survey during a Q1 positioning sprint may be stale by the time the retainer renews in Q4, while a session recording pattern from Hotjar holds longer if traffic mix is stable. Agencies that log half-lives stop recycling last year's deck as this year's strategy, and they can bill revalidation as a defined deliverable rather than an awkward scope argument.