DIAG-5 · Diagnosis · Heuristic — strong prior, re-verify periodically
Pipelines fail toward undercounting
The law
Measurement pipelines fail asymmetrically toward undercounting: dead components emit nothing, while overcounting requires an active defect (duplication, replay, bots). Conversion collapse with stable spend, clicks, and sessions is presumptively tracking loss.
Scope
Event-based conversion measurement; weakens where platforms backfill with modeled conversions. Re-verify as modeling spreads.
What this licenses you to do
On conversion collapse with stable upstream volume: audit tag/pixel/API health, consent rates, and per-source event counts before touching bids, budgets, or creative; treat sudden flat doublings as duplication defects with the same urgency.