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The Madison Avenue Field GuideA field guide to marketing & advertising, by Brandon Mina

GlossaryMeasurement & AttributionP-Value

Measurement & Attribution

P-Value

The probability of seeing a result at least as extreme as the observed one if there were truly no difference between test groups.

By Brandon MinaCEO, BrandPilot AIUpdated November 2026

Short answer

A p-value is the probability of seeing a result at least as extreme as the one observed if there were truly no difference between test groups. A small p-value suggests the result is unlikely to be due to chance alone. It does not measure the size of an effect or the probability that a hypothesis is true.