Concept Crash Course

The standalone explainers. One concept per article, reachable from any practice answer that leans on it, in no particular order.

6 reference guides. They stand on their own, so read whichever one you need.

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  1. 1Surrogate Metrics & the OECPick the one metric you'll decide by before the test starts, and a validated early signal that stands in for a long-term outcome you can't wait months to observe.
  2. 2Customer Lifetime Value (LTV)How much a customer is worth over their whole relationship with a product, not just today, and the number that decides how much you can spend to acquire them.
  3. 3Price Elasticity of DemandHow much quantity moves when you change price, and why 'raise the price, raise the revenue' is often wrong.
  4. 4Prevalence Estimation (Design-Based Sampling)How to estimate how much of a rare harm is on a platform, using probability sampling and an unbiased estimator instead of a convenience sample or a model threshold.
  5. 5Label-Error Correction (Rogan–Gladen)An imperfect labeler biases a prevalence estimate, and at low base rates a small false-positive rate can dominate. Here's the one-line correction and how to use it.
  6. 6LLM-as-Judge for MeasurementUse a large language model as a scalable labeler for measurement, with the golden-set governance and drift monitoring that make its labels trustworthy.