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Theorem

Wilks' Theorem

Probability and Statistics

Wilks' Theorem states that, under standard regularity conditions, twice the logarithm of the likelihood-ratio test statistic converges, as sample size grows, to a chi-squared distribution whose degrees of freedom equal the difference in the number of free parameters between the two nested models being compared. Named for Samuel S. Wilks, it underlies the widely used likelihood-ratio test and gives the standard asymptotic justification for treating that test statistic as coming from a chi-squared distribution.

Facts
Statement
As the sample size approaches infinity, the distribution of the test statistic -2 log(Lambda) asymptotically approaches the chi-squared distribution under the null hypothesis H0. 1
Proof Year
1938 1
Sources
1. Wilks' theorem (Wikipedia)
  • Statement of the theorem
    as the sample size approaches ∞, the distribution of the test statistic − 2 log(Λ) asymptotically approaches the chi-squared (χ²) distribution under the null hypothesis H₀
  • References, Wilks 1938
    Wilks, Samuel S. (1938). "The large-sample distribution of the likelihood ratio for testing composite hypotheses". The Annals of Mathematical Statistics.
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