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Likelihood Theory and Classical Calibration

1 · Prerequisites

2 · Summary

Quadratic-mean differentiability gives an L2 notion of smoothness for a dominated model, with a score vector and Fisher information that remain meaningful when pointwise derivatives are unavailable. Under a correct iid model, an interior true parameter, nonsingular information, a consistent measurable MLE, and a square-integrable local log-density Lipschitz envelope, the MLE has the usual asymptotic linear representation and covariance I(θ0)−1.

For a regular interior equality null whose local tangent has codimension q, the Wald, efficient-score, and likelihood-ratio statistics share the same first-order quadratic form and converge to χq2. The calibration is asymptotic and uses the stated local likelihood and score expansions. It does not apply when the null has a boundary tangent cone; the examples page works that distinction out in a normal location model.

3 · Logical flowchart

4 · Definitions, theorems and proofs

DefinitionDefinition: Literature-sourcedProof: Not applicablejudge pass (gpt-6-luna)Open item page →

Quadratic-mean differentiability at a parameter

Definition

Let P:Θ→P(X,A) be a parametric model, let Θ be open in Rd, and let a supplied sigma-finite measure μ dominate every Pθ (Parametric statistical models, Dominated statistical experiments). Supply as part of the setup a family of nonnegative finite-valued measurable functions pθ:X→[0,∞) satisfying Pθ(A)=∫Apθ dμ for every A∈A (The measure with density f relative to μ). Thus each pθ integrates to one. The density family is supplied, rather than selected from domination alone; no choice principle, joint measurability in (θ,x), or common exceptional null set is asserted. A supplied extended-valued probability density can be made finite-valued by setting it to zero on its measurable infinite-value set, which has measure zero because its integral is one. The QMD condition is unchanged by replacing any supplied density by an almost-everywhere equal version: for each fixed h, the norm in the condition below changes only on the union of two null sets. At an interior point θ0, the model is quadratic-mean differentiable (QMD) with score sθ0 if sθ0:X→Rd is measurable, Eθ0∥sθ0(X)∥2<∞, and

∫(pθ0+h−pθ0−12hTsθ0pθ0)2dμ=o(∥h∥2)

as h→0 with θ0+h∈Θ. Values of the score on {pθ0=0} do not affect this condition. The Fisher information associated with this QMD score is Iθ0=Eθ0[sθ0sθ0T]; it may be singular. QMD is an L2(μ) condition and does not assert pointwise differentiability of pθ or local mutual absolute continuity of Pθ and Pθ0.

LemmaStatement: Literature-sourcedProof: AI-adaptedprecheck passjudge pass (gpt-6-luna)Open item page →

A finite-dimensional QMD score has mean zero

Statement

Let a dominated finite-dimensional parametric model be quadratic-mean differentiable, with the supplied density family of Quadratic-mean differentiability at a parameter, at an interior point θ0∈Rd, with score sθ0∈L2(Pθ0;Rd). Then Eθ0sθ0=0.

Facts & Assumptions

Given: The dominated model, supplied density family, and QMD expansion at the interior point θ0.

[F1]

Quadratic-mean differentiability at a parameter: QMD means ∥pθ0+h−pθ0−12hTsθ0pθ0∥L2(μ)=o(∥h∥), with square-integrable score and supplied nonnegative measurable densities satisfying Pθ(A)=∫Apθ dμ.

[F2]

Cauchy-Schwarz inequality for L2: for square-integrable f,g, ∫∣fg∣ dμ≤∥f∥2∥g∥2.

[F3]

Integrating against a density agrees with integrating the product: integration of a nonnegative function against Pθ=pθ dμ equals integration of its product with pθ against μ; applying this to positive and negative parts gives the same identity for integrable real functions.

[F4]

The Lebesgue integral is linear on L1(μ): finite linear combinations of integrable real functions are integrable and their integrals are linear.

Proof

1.1F1F2F3F4algebra

Write q=pθ0 and rh=pθ0+h−q−12hTsθ0q. By [F1], ∥rh∥2=o(∥h∥). By [F3], each qh=pθ0+h is a probability square-root density, so ∥qh∥22=∥q∥22=1. Since Pθ0 is a probability and the score is square-integrable, [F2] with the constant function 1 shows its coordinates are integrable. All products in the following norm expansion are integrable by [F2], since q, rh, and hTsθ0q belong to L2(μ). Thus [F4] permits integrating the finite expansion term by term, and [F3] transfers the score term to expectation under Pθ0. Expanding qh=q+12hTsθ0q+rh gives 0=hTEθ0sθ0+2⟨q,rh⟩+∥12hTsθ0q+rh∥22. Cauchy–Schwarz [F2] bounds the inner product by o(∥h∥); square-integrability of the score and ∥rh∥2=o(∥h∥) make the last term O(∥h∥2). Thus hTEθ0sθ0=o(∥h∥).

2.1F1step 1.1algebra∎

For each coordinate vector ej, set h=tej with t>0 small enough that θ0+tej∈Θ. Divide the relation from step 1.1 by t and let t↓0 to obtain Eθ0sθ0,j=0. This holds for all j=1,…,d, hence the score vector has mean zero.

DefinitionDefinition: Literature-sourcedProof: Not applicableOpen item page →

Wald, score, and likelihood-ratio statistics for regular nulls

Definition

Assume AC for the supplied density representatives in Score and Fisher information and The Axiom of Choice. Let X1,…,Xn be iid from a dominated parametric model on an open Θ⊂Rd, and let ℓn(θ)=∑i=1nlog⁡pθ(Xi). For any nested null Θ0⊆Θ for which the maxima exist, the likelihood-ratio statistic is Ln=2{sup⁡θ∈Θℓn(θ)−sup⁡θ∈Θ0ℓn(θ)}.

For the Wald and score statistics, specialize to a regular equality null of codimension q at an interior point θ0: this is a null set which, in a C1 local parameter chart on an open neighborhood V of θ0, θ=(ψ,η)∈Rq×Rd−q, is ψ=0 near θ0=(0,η0). Its local tangent is the η-coordinate subspace. Assume the QMD information I(θ0) is positive definite. Let θ^n maximize ℓn over the full parameter space Θ and θ~n maximize it over the null Θ0, so the general likelihood-ratio definition is Ln=2{ℓn(θ^n)−ℓn(θ~n)}.

For the score statistic, assume log⁡pθ(x) is differentiable in the local chart at the parameter values where it is evaluated, and write sθ(x)=∇θlog⁡pθ(x). Require explicitly that this pointwise derivative at θ0 agrees Pθ0-almost surely with the QMD score; this compatibility is an assumption, not a consequence of QMD alone. The pointwise score and its information-matrix convention are those in Score and Fisher information.

Partition the score and information in (ψ,η) coordinates: s=(sψ,sη) and I=(IψψIψηIηψIηη),Ieff=Iψψ−IψηIηη−1Iηψ. The matrix Ieff is the information for the tested coordinates after accounting for the nuisance coordinates. If d=q, interpret empty-block products as zero, so Ieff=Iψψ=I and C below is the empty q×0 matrix. If d>q, then Iηη is positive definite; for z≠0, the quadratic form of I at (z,−Iηη−1Iηψz) equals zTIeffz>0. Thus Ieff is positive definite in either case. Put

Un(θ)=n−1/2∑i=1nsθ(Xi).

For a consistent estimator I^eff,n of Ieff and a consistent estimator C^n of C=IψηIηη−1, when θ~n∈V set Ueff,n=Uψ,n(θ~n)−C^nUη,n(θ~n). The score statistic is Sn=Ueff,nTI^eff,n−1Ueff,n. For a consistent covariance estimator V^ψ,n of the ψ-block of I−1, when θ^n∈V the Wald statistic is Wn=nψ^nTV^ψ,n−1ψ^n, where ψ^n is the tested coordinate of θ^n. Set Wn=0 when θ^n∉V and Sn=0 when θ~n∉V, without evaluating coordinates or scores outside the chart. When a displayed inverse does not exist, set that statistic to zero. Under the regularity conditions used in the later calibration theorem, consistency places both maximizers in V and the estimated inverses exist with probability tending to one. This definition gives the statistics and their normalizations; it asserts no finite-sample or asymptotic distribution.

TheoremStatement: Literature-sourcedProof: AI-adaptedprecheck passjudge pass (gpt-6-luna)Open item page →

Asymptotic linearity and normality of a regular MLE

Statement

Assume the Axiom of Choice. Let X1,X2,… be iid with law Pθ0 in a dominated parametric model {Pθ:θ∈Θ}, where Θ is open in Rd, d≥1, and θ0∈Θ. Let pθ be densities with respect to one supplied sigma-finite measure. Suppose the model is QMD at θ0 with score sθ0 and positive-definite information I=Eθ0[sθ0sθ0T]. Assume there are a neighborhood V of θ0 and a nonnegative measurable L with Eθ0L2<∞ such that, on one Pθ0-full set,

∣log⁡pθ1(x)−log⁡pθ2(x)∣≤L(x)∥θ1−θ2∥(θ1,θ2∈V).

Suppose a measurable exact MLE θ^n exists and is consistent, in the sense that Pθ0(∥θ^n−θ0∥>ε)→0 for every ε>0. Then n(θ^n−θ0)=I−11n∑i=1nsθ0(Xi)+oPθ0(1) ⇒ Nd(0,I−1). Under the same local hypotheses, every consistent measurable exact likelihood maximizer over a possibly n-dependent subset that contains θ0 is also root-n bounded in probability. The conclusion is asymptotic; it gives no exact finite-sample normal law.

Facts & Assumptions

Given: The iid dominated model, QMD score and information, local envelope, consistent measurable exact MLE, and Axiom of Choice in the statement.

[F1]

Parametric statistical models: a parametric model is the supplied map θ↦Pθ on an experiment.

[F2]

Dominated statistical experiments: domination means every Pθ is absolutely continuous with respect to one supplied sigma-finite measure.

[F3]

Quadratic-mean differentiability at a parameter: QMD means the square-root densities have the stated L2(μ) first-order expansion with score sθ0.

[F4]

Stochastic order and convergence notation for finite-dimensional random vectors: oP(1) is convergence in probability to zero, and OP(1) is boundedness in probability in finite-dimensional Euclidean norm.

[F5]

Finite-dimensional stochastic-order calculus and tightness: finite-dimensional convergence in distribution implies boundedness in probability; products of a vanishing factor and a bounded factor vanish in probability.

[F6]

Vector Slutsky theorem: if Yn−c=oP(1) and Xn⇒X, then (Xn,Yn)⇒(X,c), with continuous maps preserving this limit.

[F7]

Multivariate iid central limit theorem: under AC, iid finite-second-moment vectors satisfy the multivariate CLT, including singular covariance.

[F8]

Multivariate normal law, including singular covariance: under AC, Nd(m,Σ) exists for each finite-dimensional symmetric positive-semidefinite covariance Σ.

[F9]

Cauchy-Schwarz inequality for L2: for square-integrable g,h, E0∣gh∣≤(E0g2)1/2(E0h2)1/2.

[F10]

Dominated convergence: pointwise almost-everywhere convergence under an integrable dominating function permits passing limits through the integral.

[F11]

Chebyshev-Markov inequality for the integral: for measurable Y≥0 and a>0, P0(Y≥a)≤E0Y/a.

[F12]

A finite-dimensional QMD score has mean zero: the score of a finite-dimensional parametric QMD model at an interior point has mean zero under that point's law.

[A1]

The Axiom of Choice: AC is assumed for the multivariate CLT and Gaussian-law suppliers [F7]–[F8].

[A2]

The score and information are those in [F3]; I is positive definite.

[A3]

The local log-density envelope and consistency/MLE hypotheses are as in the Statement.

Proof

1.1A2F1F2F3F9F12algebra

Write P0=Pθ0, S0={pθ0>0}, and rt=pθ0+t−pθ0−12tTsθ0pθ0. By [F3], ∥rt∥L2(μ)=o(∥t∥), and [F12] gives E0sθ0=0. On S0c both pθ0 and sθ0pθ0 vanish, so the probability mass αt=∫S0cpθ0+t dμ is o(∥t∥2). Expanding the QMD approximation in [F3] and applying [F9] to its cross term gives ∥pθ0+t−pθ0∥22=14tTIt+o(∥t∥2).

2.1A2A3F2F3F9F10step 1.1algebra

Normalize the absolutely continuous part on S0 by qt=pθ0+t1S0/(1−αt), and put at=qt/pθ0−1 on S0. Since αt=o(∥t∥2), [F3] gives at=12tTsθ0+oL2(P0)(∥t∥), so E0at2=14tTIt+o(∥t∥2) and 2E0at+E0at2=0 from E0(1+at)2=1. The local envelope makes ft=log⁡(pθ0+t/pθ0) square-integrable on S0 and ∥ft∥2=O(∥t∥). Along every sequence t→0 with t/∥t∥→u, the L2 convergence of at/∥t∥ has an almost-everywhere convergent subsequence. On it, 2log⁡(1+at)/∥t∥→uTsθ0 pointwise. Since ∣ft∣/∥t∥≤L and sθ0∈L2(P0), ∣ft/∥t∥−uTsθ0∣2≤2L2+2∥sθ0∥2; dominated convergence [F10] gives convergence in L2 along that subsequence. Every subsequence has such a subsubsequence, so convergence holds for the full sequence. Sequential compactness of the unit sphere therefore yields ft=tTsθ0+oL2(P0)(∥t∥). Moreover, the squares at2/∥t∥2 are uniformly integrable because at/∥t∥ converges in L2 along every convergent direction. Taking the logarithm expansion in expectation requires a tail check. Fix ε>0. On ∣at∣≤ε, the Taylor remainder 2log⁡(1+at)−2at+at2 is bounded by ω(ε)at2, where ω(ε)→0. Uniform integrability gives E0[at21∣at∣>ε]=o(∥t∥2) and therefore P0(∣at∣>ε)=o(∥t∥2). On this tail, ∣2log⁡(1+at)∣≤∣ft∣+∣log⁡(1−αt)∣; its expectation is o(∥t∥2) by the envelope, Cauchy–Schwarz [F9], and the tail probability. The tail expectations of ∣at∣ and at2 are also o(∥t∥2) by [F9] and uniform integrability. Letting ε↓0 proves that the expected Taylor remainder is o(∥t∥2). Taking expectations then gives E0ft=2E0at−E0at2+o(∥t∥2)=−12tTIt+o(∥t∥2); the normalization term log⁡(1−αt) is o(∥t∥2).

2.2step 1.1algebra

The squared Hellinger distance H2(Pθ0+t,P0)=∫(pθ0+t−pθ0)2dμ equals 14tTIt+o(∥t∥2) by step 1.1. The affinity ρt=∫pθ0+tpθ0dμ=1−H2/2. On S0 let Y=pθ0+t/pθ0, so E0Y=ρt. For y>0, log⁡y≤log⁡ρt+(y−ρt)/ρt follows from z−1−log⁡z≥0 for z=y/ρt, since this function has derivative 1−1/z and its minimum is 0 at z=1; integrating gives P0ft=2E0log⁡Y≤2log⁡ρt. Since log⁡(1−x)≤−x for 0≤x<1 because −x−log⁡(1−x) has derivative x/(1−x)≥0 and value 0 at x=0. Thus 2log⁡ρt≤−H2, so for some c,δ>0, P0ft≤−c∥t∥2 whenever ∥t∥≤δ0.

3.1A3F3F4step 2.1construct

Let Gnf=n(Pnf−P0f) for the empirical measure Pn. The pointwise Lipschitz envelope gives ∥ft−fv∥L2(P0)≤∥L∥2∥t−v∥. The sample and mean processes are continuous in t on compact local balls, so their suprema equal suprema over countable dense subsets and are measurable. To bound the local supremum, take an independent ghost sample X1′,…,Xn′. For each fixed original sample, the supremum of absolute values is convex in the ghost sample vector, so Jensen's inequality replaces P0f by n−1∑if(Xi′) in the expected supremum. Swapping each pair (Xi,Xi′) with an independent sign and then using the triangle inequality bounds that supremum by twice the expected conditional Rademacher supremum. Condition on the observations for the latter. For the conditional Rademacher process Rn(f)=n−1/2∑iϵif(Xi), Hoeffding's exponential bound Eϵeλ(Rn(f)−Rn(g))=∏icosh⁡(λ(f−g)(Xi)/n)≤exp⁡{λ2Pn(f−g)2/2}, since log⁡cosh⁡u≤u2/2 (integrate tanh⁡u≤u for u≥0 and use evenness), makes each increment sub-Gaussian with variance proxy Pn(f−g)2≤PnL2∥t−v∥2. Choose successively finer dyadic Euclidean nets of the radius-r parameter ball. At level k the net has at most (C2k)d points, each increment from its level-(k−1) parent has scale at most Cr2−k(PnL2)1/2, and the expected maximum of N centered sub-Gaussian variables of scale σ is at most σ2log⁡(2N), by the exponential-moment bound and optimizing λ. Summing the resulting bounds uses the convergent series ∑k≥12−kk and gives Eϵsup⁡∥t∥≤r∣Rn(ft−f0)∣≤Cdr(PnL2)1/2. Symmetrization and E(PnL2)1/2≤(P0L2)1/2 therefore give Esup⁡∥t∥≤r∣Gn(ft−f0)∣≤Cdr∥L∥2. For rt=ft−tTsθ0, step 2.1 gives sup⁡∥t∥≤M/nP0rt2=o(n−1), and increments have the square-integrable pointwise envelope L+∥sθ0∥. Fix a mesh ε>0 and cover the bounded h-ball by finitely many mesh-ε points. At each center hj, the variance of nGnrhj/n is nVar⁡0(rhj/n)≤nP0rhj/n2=o(1), so Chebyshev and finiteness of the net make the maximum over centers oP(1). For increments within cells, form gh=rh/n−rhj/n, where hj is the center of the cell containing h. Each gh is pointwise bounded by ε(L+∥sθ0∥)/n. Apply conditional Rademacher chaining to the union of cell classes: at dyadic level k there are at most CMε−d2kd links, each with conditional scale at most Cε2−k(Pn(L+∥sθ0∥)2)1/2 after the n normalization. The exponential maximum bound and summation of ∑k≥02−klog⁡(CMε−d)+Cdk give an expected supremum at most CMεlog⁡(CM/ε) after symmetrization and E(Pn(L+∥sθ0∥)2)1/2≤∥L+∥sθ0∥∥2. Markov's inequality then shows that these cell increments vanish in probability as ε↓0. Letting n→∞ and then ε↓0 proves sup⁡∥h∥≤M∣nGnrh/n∣=oP(1). Thus, for each fixed M, uniformly over ∥h∥≤M, ℓn(θ0+h/n)−ℓn(θ0)=hTΔn−12hTIh+oP0(1),Δn=n−1/2∑i=1nsθ0(Xi). The expectation term is step 2.1; the centered term follows by writing ft=tTsθ0+(ft−tTsθ0) and using the two net bounds.

4.1A3F4F11step 3.1step 2.2algebra

Reduce δ0 if needed so the log envelope holds on the radius 2δ0 ball, and put δ=δ0/2. Consistency makes θ^n lie within δ of θ0 with probability tending to one. On the dyadic shells rj≤∥t∥≤2rj with rj=2jM/n, exact maximization and ℓn(θ^n)≥ℓn(θ0) require nsup⁡∥t∥≤2rj∣Gnft∣≥cnrj2. The expectation bound in step 3.1 and Markov's inequality [F11] bound the probability of this event by C/(nrj)=C/(2jM). Summing the geometric series and then letting M→∞ proves n(θ^n−θ0)=OP0(1) using [F4]. The argument used only consistency, feasibility of θ0, and the maximizing inequality; it therefore proves the same bound for any exact maximizer over a subset containing θ0.

5.1A3F4F5F7step 3.1step 4.1algebra

Put h^n=n(θ^n−θ0) and hn∗=I−1Δn. The multivariate CLT [F7] and [F5] make hn∗=OP0(1); step 4.1 makes h^n=OP0(1). For Qn(h)=hTΔn−12hTIh, Qn(hn∗)−Qn(h)=12(h−hn∗)TI(h−hn∗)≥12λmin⁡(I)∥h−hn∗∥2. Uniform convergence on bounded balls in step 3.1, feasibility of bounded local h because θ0 is interior, and exact MLE maximization therefore force h^n−hn∗=oP0(1).

6.1A1A2F4F6F7F8step 5.1∎

The CLT [F7] gives Δn⇒Nd(0,I); the limiting law exists by [F8]. Since I is invertible, hn∗=I−1Δn⇒Nd(0,I−1) by the continuous linear map. Combining this with step 5.1 by [F6] proves both the asymptotic linear representation and the stated normal limit. AC is used only through [F7]–[F8].

TheoremStatement: Literature-sourcedProof: AI-adaptedprecheck passOpen item page →

Wald, score, and likelihood-ratio asymptotic chi-square calibration

Statement

Assume AC. Let X1,…,Xn be iid from Pθ0 in a correctly specified dominated model, with θ0=(0,η0) an interior point of the full open parameter set Θ⊂Rq×Rd−q. In a local C1 parameter chart, suppose the null is ψ=0, so its local null set is a linear subspace of codimension q≥1; all score and information coordinates below use this chart. Assume QMD at θ0 with positive-definite information

I=(IψψIψηIηψIηη),

and write Ieff=Iψψ−IψηIηη−1Iηψ. If d=q, interpret nuisance blocks as empty, so Ieff=Iψψ=I and products involving η are zero. Let Δn=n−1/2∑isθ0(Xi). Assume the hypotheses of Asymptotic linearity and normality of a regular MLE hold for the full model. Assume the constrained MLE is measurable, exact, consistent, and maximizes over a set containing θ0; it is root-n bounded by that theorem's localization conclusion. For every finite M the following likelihood and score expansions hold uniformly over ∥h∥≤M:

ℓn(θ0+h/n)−ℓn(θ0)=hTΔn−12hTIh+oP(1), n−1/2∇ℓn(θ0+h/n)=Δn−Ih+oP(1).

Assume the covariance, score-projection, and efficient-information estimators in Wald, score, and likelihood-ratio statistics for regular nulls converge in probability to their stated limits. Partition Δn=(Δψ,n,Δη,n), put rn=Δψ,n−IψηIηη−1Δη,n, and set Tn=rnTIeff−1rn. Then, under the null,

Wn=Tn+oP(1),Sn=Tn+oP(1),Ln=Tn+oP(1),Wn⇒χq2,Sn⇒χq2,Ln⇒χq2.

Here χq2 is the law defined in Chi-square laws, including zero degrees. This is an asymptotic calibration; no exact finite-sample chi-square law is asserted.

Facts & Assumptions

Given: The iid correctly specified model and the local-null, QMD, positive-information, consistency, local-expansion, estimator, and covariance hypotheses in the Statement. Assume AC.

[F1]

Quadratic-mean differentiability at a parameter: QMD supplies the score sθ0 and information matrix I=Eθ0[sθ0sθ0T].

[F2]

Wald, score, and likelihood-ratio statistics for regular nulls: in local coordinates (ψ,η), Wn uses the tested MLE coordinates and their covariance, Sn uses the consistent estimated efficient score and information, and Ln is twice the unrestricted-minus-restricted log likelihood.

[F3]

Asymptotic linearity and normality of a regular MLE: under its local envelope and consistency hypotheses, the full MLE has the stated asymptotic linear representation, and any consistent exact restricted maximizer containing θ0 is root-n bounded.

[F4]

Stochastic order and convergence notation for finite-dimensional random vectors: boundedness in probability and convergence in probability use the finite-dimensional Euclidean norm.

[F5]

Finite-dimensional stochastic-order calculus and tightness: a vector converging in distribution is bounded in probability, and products of bounded and vanishing vectors vanish in probability.

[F6]

Vector Slutsky theorem: a continuous map of a weakly convergent vector and a vector converging in probability to a constant has the corresponding weak limit.

[F7]

Multivariate iid central limit theorem: under AC, the normalized sum of iid finite-second-moment vectors converges to a multivariate normal with their covariance.

[F8]

Multivariate normal law, including singular covariance: under AC, Nd(0,I) has covariance I and its linear maps are multivariate normal.

[F9]

Chi-square laws, including zero degrees: for q≥1, χq2 is the law of ∑j=1qGj2=∥G∥2 when G∼Nq(0,Iq) has independent standard-normal coordinates.

[A1]

The local likelihood and normalized score expansions are assumed uniformly on each bounded local parameter set as stated; QMD alone is not used to infer them here.

[A2]

I is positive definite and 1≤q≤d; when q=d, the nuisance blocks are empty and their products are interpreted as zero.

[A3]

The Axiom of Choice: AC is inherited from the density-representative convention in [F2], the MLE theorem [F3], and the probability-law suppliers [F7]–[F9].

Proof

1.1A2A3F1F6F7F8givenalgebra

If d=q, then Ieff=I is positive definite. If d>q, Iηη is a positive-definite principal block. For nonzero v∈Rq, evaluate the quadratic form of I at (v,−Iηη−1Iηψv); the result is vTIeffv>0, so Ieff is positive definite in either case. Normalizing pθ0+h in the QMD expansion [F1], write pθ0+h=pθ0+12hTsθ0pθ0+eh with ∥eh∥L2(μ)=o(∥h∥). Expanding the squared norm, whose value is ∫pθ0+hdμ=1, gives hTEθ0sθ0+O(∥h∥2)+o(∥h∥)=0. Taking h=tej and dividing by t proves each score coordinate has mean zero. Since sθ0 is square integrable by [F1], the iid CLT [F7] gives Δn⇒Nd(0,I) under AC. Define rn=Δψ,n−IψηIηη−1Δη,n. Its covariance, by block multiplication, is Var⁡(rn)=Iψψ−IψηIηη−1Iηψ−IψηIηη−1Iηψ+IψηIηη−1IηηIηη−1Iηψ=Ieff. Thus the linear-map case of Slutsky [F6] gives rn⇒Nq(0,Ieff); its covariance is the block calculation above.

2.1A1A2F3F4step 1.1algebra

By [F3], the full MLE satisfies n(θ^n−θ0)=I−1Δn+oP(1). Solving the block system I(a,b)T=(Δψ,n,Δη,n)T shows its tested block is a=Ieff−1rn, including the empty-nuisance case. If d=q, the local null contains only θ0, so consistency makes the constrained MLE equal to θ0 with probability tending to one and there is no nuisance expansion to prove. Otherwise, [F3] makes the constrained root-n error bounded. In local coordinates h=(u,v) for (η,ψ), the limiting quadratic log likelihood is Qn(u,v)=uTΔη,n+vTΔψ,n−12{uTIηηu+2uTIηψv+vTIψψv}. For general v, completing the square in u gives the unique maximizer u=Iηη−1(Δη,n−Iηψv) and the profile vTrn−12vTIeffv up to a term independent of v. At the null v=0 this gives the unique nuisance maximizer u0=Iηη−1Δη,n. On every distance-ε set from u0, strict positive definiteness of Iηη makes the quadratic log likelihood at least 12λmin⁡(Iηη)ε2 below its maximum. Uniformity of the likelihood expansion [A1], constrained root-n tightness [F3], and this gap therefore give n(η~n−η0)=Iηη−1Δη,n+oP(1).

3.1A1A2F2F4step 2.1algebra

Consistency places both maximizers in the open chart neighborhood with probability tending to one; the off-chart zero conventions in [F2] therefore do not affect the expansions below. The upper-left block of I−1 is Ieff−1 by solving the block system I(x,y)T=(a,0)T. The differentiable local chart has tested coordinate ψ, so the Wald statistic in [F2], the expansion in step 2.1, and covariance consistency give Wn=(Ieff−1rn)TIeff(Ieff−1rn)+oP(1)=rnTIeff−1rn+oP(1).

3.2A1A2F2F4F5step 2.1algebra

If d=q, the nuisance score is empty and the score expansion [A1] at h=0 gives Ueff,n=Uψ,n(θ0)=Δn+oP(1)=rn+oP(1). If d>q, the score expansion [A1] at the constrained MLE and n(η~n−η0)=Iηη−1Δη,n+oP(1) give Uψ,n(θ~n)=rn+oP(1) and Uη,n(θ~n)=oP(1). The estimated projection coefficient is bounded in probability by consistency, so the efficient score in [F2] is rn+oP(1). Efficient-information consistency and [F5] imply Sn=rnTIeff−1rn+oP(1).

3.3A1A2F2F4F5step 2.1algebra

The likelihood expansion in [A1] makes Ln equal, up to oP(1), twice the maximum of Qn(u,v) over all local (u,v) minus twice its maximum over the null v=0. The unrestricted and restricted quadratic maximizers are linear functions of Δn, hence are OP(1) by step 1.1 and [F5]. Taking a bounded local ball large enough with probability arbitrarily close to one justifies using the uniform expansions for both maxima. The profile formula in step 2.1 reduces this difference to 2sup⁡v{vTrn−12vTIeffv}=rnTIeff−1rn. The identity follows by completing the square at v=Ieff−1rn. Hence Ln=rnTIeff−1rn+oP(1).

4.1A3F4F5F6F7F8F9step 1.1step 3.1step 3.2step 3.3∎

Since rn⇒Nq(0,Ieff) and Ieff is positive definite, its transformed vector Ieff−1/2rn converges to Nq(0,Iq). The squared Euclidean norm of that limit is χq2 by [F9]. Combining this with steps 3.1–3.3 and [F4]–[F5] proves all three limits and their common first-order approximation. AC is inherited through [F2], [F3], and [F7]–[F9], as recorded in [A3].

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First-order equivalence of Wald, score, and likelihood-ratio statistics

Statement

Assume AC and the hypotheses of Wald, score, and likelihood-ratio asymptotic chi-square calibration. Under the null, the three statistics satisfy Wn−Sn=oP(1), Sn−Ln=oP(1), and Ln−Wn=oP(1). Hence they have the same first-order null calibration, namely χq2.

Facts & Assumptions

[F1]

Wald, score, and likelihood-ratio asymptotic chi-square calibration: all three statistics equal one common quadratic score form up to oP(1), and that form converges to χq2.

[A1]

The Axiom of Choice: AC is inherited from [F1], whose iid score CLT uses the multivariate iid CLT.

Proof

1.1A1F1algebra

By [F1], there is a common random quadratic form Tn with Wn=Tn+oP(1), Sn=Tn+oP(1), and Ln=Tn+oP(1). Subtracting the first two equalities and applying the triangle inequality gives Wn−Sn=oP(1); subtracting the second and third gives Sn−Ln=oP(1); subtracting the third and first gives Ln−Wn=oP(1).

2.1F1step 1.1∎

Theorem [F1] states Tn⇒χq2 and each statistic has that same limit under the theorem's hypotheses. The differences proved in step 1.1 therefore express first-order equivalence, not exact finite-sample equality.

5 · Examples, counterexamples and false statements

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