Asymptotic Methods in Statistical Inference - Statistics Centre

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174 Theorem: Under (C1)-(C5) there exists a sequence ˆ = ˆ ( 1 ) of roots of the likelihood equation such that (i) ³ˆ is a local maximum of ()´ → 1and (ii) ˆ → 0 . Proof: Let0 be small enough that 0 − 0 + ¯, but otherwise arbitrary. (Is this possible? Why?) In the notation of the lemma, define = ( 0 − ) ∩ ( 0 + ). Then 0 (X ∈ ) → 1. For x ∈ there exists ∗ ∈ ( 0 − 0 + ) at which (|x) has a local maximum. This establishes the existence of a sequence ∗ = () ∗ ofrootsof 0 (|x) = 0, corresponding to local maxima, with 0 (| ∗ − 0 | ) → 1 We cannot yet conclude that ∗ → 0 ,becauseofthe dependence on . However, define ˆ to be that root, corresponding to a local maximum, which is closest to ¯ 0 . Then (with probability approaching 1) ¯ˆ − 0¯¯¯ , andˆ does not depend on the choice of , sothat ˆ → 0 . ¤
175 • Under stronger conditions one can show the existence and consistency of the MLE, i.e. of a global maximum of (). However, one typically computes a root ˆ of the likelihood equation which may be only a local maximum. Corollary: Withconditionsasabove,if 0 () has a unique zero ˆ for all (sufficiently large) and all 1 then: (i) ˆ → 0 ; (ii) ³ˆ is the MLE´ → 1as →∞. Proof: (i): The uniqueness implies that the zeros ˆ of 0 () correspond to the ˆ in the statement of the theorem. (ii): With probability tending to 1, ˆ is at least a local maximum, not a saddlepoint or a minimum. Suppose that ˆ is only a local maximum, and not ¡ the MLE. Then we must have 0 ¢ ³ˆ ´ for some 0 6= ˆ ; then there is a local minimum between them at which 0 = 0, contradicting the uniqueness of ˆ . Thus (with probability tending to 1) ˆ is the global maximizer, i.e. is the MLE.
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STATISTICS 665 ASYMPTOTIC METHODS I
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II LARGE-SAMPLE INFERENCE 42 5 Intr
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V LIKELIHOOD METHODS 169 19 Maximum
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Part I PROBABILISTIC PRELIMINARIES
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The ‘rate’ of convergence refer
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11 imagine ‘large’ but remain
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13 • For the ( ) distribution,
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15 —Corollary1: → If h (
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17 2. Slutsky’s Theorem; conseque
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— By the CLT, − q (1 − ) 1
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21 • Corollary 1: If → the
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23 • First an application. Let 2
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25 with d.f. (), then there is a
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27 next lecture), = 1− " ( )+
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29 • CLT via the Edgeworth expans
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31 (why?) with ‘cumulant generati
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Thus in (3.2), () () isthec.f.of
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35 • Delta method. Suppose that
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37 • Uniformity—read§2.6 • C
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39 suppose that → 0. Then X =1
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41 • Under this condition ˆ is (
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43 5. Introduction to asymptotic te
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45 • We often work instead with t
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47 • Two-sample problems. Suppose
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49 • Example 2: 1 ∼ P(),
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51 term is Ã √ ˆ ( ( 0 )
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53 • More useful is to study the
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55 • Example: t-test of a mean.
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57 • Efficacy. Test : = 0 vs.
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59 Put = − and test for tre
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61 7. Relative efficiency • Relat
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• The constraint (1) ∼ (2)
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65 =1. Theefficacy is = 0 q (0)
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67 • Example 3. In this example
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69 Proof of ‘ 1’: From 1 − (
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71 • We will consider only ‘lev
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73 • Example 1. Suppose we (mista
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75 To see this take 0 = 0 for simp
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77 The numerator of is normally d
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79 9. Confidence intervals • X =(
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81 • Example. 1 ∼ () ( 0);
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83 • A strong CI on a population
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85 • A more involved example of a
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87 We exhibit 1 () 2 () → 1−
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10. Point estimation; Asymptotic re
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91 Recall that if 0 () 6= 0 (assum
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93 where (with being a bound on |
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• Asymptotic Relative Efficiency.
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97 0.0 0.1 0.2 0.3 0.4 0.5 0.6 -3 -
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99 that then √ ³ ¯ − ´
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101 — This is also the ARE of the
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103 We minimize Z h 2 ()+2 2 ()
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105 In a broad class of cases, comp
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107 The ARE of the estimates consid
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109 We have lim →∞ { ∗ () −
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111 13. Random vectors; multivariat
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113 • X () () → c (constant)
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115 • Multivariate normality. We
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117 • If X ∼ (μ Σ) then an
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119 14. Multivariate applications
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121 One can eliminate the last elem
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Page 127 and 128: 127 Proof: Write Then +1 = − X
Page 129 and 130: 129 15. Expectation functionals; U-
Page 131 and 132: 131 • A closely related estimate,
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Page 135 and 136: 135 • Rao-Blackwell Theorem: We c
Page 137 and 138: 137 • Here we get the variance of
Page 139 and 140: 139 16. Asymptotic normality of U-s
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Page 143 and 144: 143 • Proofofclaim1: [( − ) |
Page 145 and 146: 145 • V-statistics. Recall that i
Page 147 and 148: 147 17. Influence function analysis
Page 149 and 150: 149 By using the fact that | 2 −
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Page 153 and 154: 153 By the CLT and Slutsky’s theo
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Page 157 and 158: 157 18. Bootstrapping • Suppose t
Page 159 and 160: 159 • In each of the examples abo
Page 161 and 162: 161 • Example 2. ( )=bias. Writ
Page 163 and 164: 163 • For the measure (18.1) we t
Page 165 and 166: 165 (True for functionals (·) con
Page 167 and 168: 167 • Indeed, since ( ) has plu
Page 169 and 170: 169 Part V LIKELIHOOD METHODS
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Page 173: 173 • Assume: (C1) Identifiabilit
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Page 179 and 180: 179 • Information Inequality. (Cr
Page 181 and 182: 181 • Example: 1 the indicator
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Page 187 and 188: 187 Claim: (i) (ii) (iii) 0 ( 0 )
Page 189 and 190: 189 Define the ‘scores’ ( −
Page 191 and 192: 191 • The MLE is not the only eff
Page 193 and 194: 193 The variance-minimizing choice
Page 195 and 196: 195 • Multiparameter likelihood e
Page 197 and 198: 197 • Efficiency. Under appropria
Page 199 and 200: 199 asymptotic normality of the sam
Page 201 and 202: 201 • Likelihood ratio test. Put
Page 203 and 204: 203 and 000 ( ∗∗ ) is (1)
Page 205 and 206: 205 • Example. 1 ∼ Logistic,
Page 207 and 208: 207 • Multiparameter inferences.
Page 209 and 210: 209 For testing, I( 0 ) is replaced
Page 211 and 212: 211 24. Examples Example: 1 ∼
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Page 215 and 216: 215 • The likelihood ratio statis
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Page 219 and 220: 219 The parameter vector is θ = ³
Page 221 and 222: 221 25. Higher order asymptotics
Page 223 and 224: 223 As in Lecture 10, cov h i 2 h
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225 • The normal approximation, a
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227 By uniqueness of m.g.f.s, (;
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229 • Example 2. Let = P 1 w
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231 • The error of Saddlepoint
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