Neyman-Pearson lemma

Etymology
Named after Jerzy Neyman and Egon Pearson.

Proper noun

 * 1)  A lemma stating that when performing a hypothesis test between two point hypotheses H0: θ = θ0 and H1: θ = θ1, then the likelihood-ratio test which rejects H0 in favour of H1 when $$\Lambda(x)=\frac{ L( \theta _0 \mid x)}{ L (\theta _1 \mid x)} \leq \eta$$ where $$P(\Lambda(X)\leq \eta\mid H_0)=\alpha$$ is the most powerful test of size &alpha; for a threshold η.