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Mathematical Statistics II

Formula sheet

Definitions and key results, unit by unit.

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  1. Unit 1: Neyman-Pearson testing and power
  2. Unit 2: Consistency, asymptotic normality, and delta methods
  3. Unit 3: Bayesian inference and decision rules
  4. Unit 4: Linear models and projection geometry
  5. Unit 5: Rank and distribution-free methods
  6. Unit 6: Bootstrap, permutation, and simulation-based inference

Unit 1

Neyman-Pearson testing and power

Framework

Hypotheses and tests

Test H0 ⁣:θ∈Θ0H_0\colon \theta \in \Theta_0 against H1 ⁣:θ∈Θ1H_1\colon \theta \in \Theta_1 (disjoint). A test is a rejection region RR, or a test function ϕ(x)∈[0,1]\phi(\mathbf{x}) \in [0,1] giving the probability of rejecting.

Type I and Type II errors

Type I: rejecting H0H_0 when it is true. Type II: failing to reject H0H_0 when H1H_1 is true.

Power function

β(θ)=Pθ(X∈R)=Eθ[ϕ(X)]\beta(\theta) = P_\theta(\mathbf{X} \in R) = E_\theta\big[\phi(\mathbf{X})\big]

For θ∈Θ0\theta \in \Theta_0 it is the Type I error rate; for θ∈Θ1\theta \in \Theta_1 it is one minus the Type II error rate.

Size and level

size=sup⁡θ∈Θ0β(θ),level α  ⟺  size≤α\text{size} = \sup_{\theta \in \Theta_0} \beta(\theta), \qquad \text{level } \alpha \iff \text{size} \le \alpha

p-value

p(x)=sup⁡θ∈Θ0Pθ(T(X)≥T(x))p(\mathbf{x}) = \sup_{\theta \in \Theta_0} P_\theta\big(T(\mathbf{X}) \ge T(\mathbf{x})\big)

For a test that rejects for large TT. Reject at level α\alpha exactly when p≤αp \le \alpha. For a simple null and continuous TT, p(X)∼Unif(0,1)p(\mathbf{X}) \sim \mathrm{Unif}(0,1) under H0H_0. It is not the probability that H0H_0 is true.

Optimal tests

Uniformly most powerful test

A level-α\alpha test whose power is at least that of every other level-α\alpha test at every θ∈Θ1\theta \in \Theta_1.

Neyman–Pearson lemma

ϕ(x)={1,f(x;θ1)>k f(x;θ0)γ,f(x;θ1)=k f(x;θ0)0,f(x;θ1)<k f(x;θ0)\phi(\mathbf{x}) = \begin{cases} 1, & f(\mathbf{x};\theta_1) > k\,f(\mathbf{x};\theta_0) \\ \gamma, & f(\mathbf{x};\theta_1) = k\,f(\mathbf{x};\theta_0) \\ 0, & f(\mathbf{x};\theta_1) < k\,f(\mathbf{x};\theta_0) \end{cases}

For simple H0 ⁣:θ=θ0H_0\colon \theta = \theta_0 versus simple H1 ⁣:θ=θ1H_1\colon \theta = \theta_1, with k≥0k \ge 0 and γ\gamma chosen so that Eθ0[ϕ]=αE_{\theta_0}[\phi] = \alpha, this likelihood-ratio test is most powerful at level α\alpha.

Monotone likelihood ratio

The family has MLR in T(x)T(\mathbf{x}) if for every θ1<θ2\theta_1 < \theta_2 the ratio f(x;θ2)/f(x;θ1)f(\mathbf{x};\theta_2)/f(\mathbf{x};\theta_1) is a nondecreasing function of T(x)T(\mathbf{x}). A one-parameter exponential family with w(θ)w(\theta) increasing has MLR in ∑it(xi)\sum_i t(x_i).

UMP one-sided test (Karlin–Rubin)

ϕ(x)=1{T(x)>c},Pθ0(T>c)=α\phi(\mathbf{x}) = \mathbf{1}\{T(\mathbf{x}) > c\}, \qquad P_{\theta_0}(T > c) = \alpha

With MLR in TT, this is UMP of level α\alpha for H0 ⁣:θ≤θ0H_0\colon \theta \le \theta_0 versus H1 ⁣:θ>θ0H_1\colon \theta > \theta_0. For discrete TT, randomize at T=cT = c to get size exactly α\alpha. Two-sided alternatives usually have no UMP test.

Likelihood ratio test

Λ(x)=sup⁡θ∈Θ0L(θ;x)sup⁡θ∈ΘL(θ;x),reject H0 when Λ(x)≤c\Lambda(\mathbf{x}) = \frac{\sup_{\theta \in \Theta_0} L(\theta;\mathbf{x})}{\sup_{\theta \in \Theta} L(\theta;\mathbf{x})}, \qquad \text{reject } H_0 \text{ when } \Lambda(\mathbf{x}) \le c

0≤Λ≤10 \le \Lambda \le 1. The denominator uses the unrestricted MLE and the numerator the MLE under H0H_0.

Duality of tests and confidence sets

C(x)={θ0:x∈A(θ0)},θ0∈C(x)  ⟺  x∈A(θ0)C(\mathbf{x}) = \big\{\theta_0 : \mathbf{x} \in A(\theta_0)\big\}, \qquad \theta_0 \in C(\mathbf{x}) \iff \mathbf{x} \in A(\theta_0)

If, for each θ0\theta_0, the acceptance region A(θ0)A(\theta_0) gives a level-α\alpha test of H0 ⁣:θ=θ0H_0\colon \theta = \theta_0, then Pθ(θ∈C(X))≥1−αP_\theta\big(\theta \in C(\mathbf{X})\big) \ge 1 - \alpha for every θ\theta: CC is a 1−α1-\alpha confidence set. Conversely, a 1−α1-\alpha confidence set CC gives the level-α\alpha acceptance regions A(θ0)={x:θ0∈C(x)}A(\theta_0) = \{\mathbf{x} : \theta_0 \in C(\mathbf{x})\}.

Unit 2

Consistency, asymptotic normality, and delta methods

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Unit 3

Bayesian inference and decision rules

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Unit 4

Linear models and projection geometry

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Unit 5

Rank and distribution-free methods

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Unit 6

Bootstrap, permutation, and simulation-based inference

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