63
* 3.4 Influencefunction
andasymptotic distribution
Theone-dimensional a
case
• h T
X ,...,
1X i→
nt
,consistency ∞
Functional
• h T
i F
. Appliedto
data:
T b F D
n
E
.
consistency:
T b F D
n
E
→ h T
i F
Central
•
limittheorem:
T b F D
n
E
≈∼N h
h T i F ,v i /n
= v E
h IF
; X T, i F
2.
64
Modelwith
•
density
h f i x,θ
Maximum
− →
likelihood est.
Moregener
•
al:M-estimators
P ψ
iD X ,
ib θ E
=0
Functional:
ψ R h i x,θ
h dF i x
=0
MLE:
h ψ i x,θ
∂
= log
∂θh h f ii x,θ
sh =:
i x,θ
.
• IFhx;
i F
1
= ψ
chx,θ i
= c
∂
R ψ
∂θhx,θ i h f i x,θ
= dx R −
h ψ i x,θ
sh i x,θ
h f i x,θ
dx
65 3.4 Morethan b
onepar ameter
andpossib lymore
thanone
X
• h T
X ,...,
1X i→
nt
,consistency ∞
Functional
• h T
i F
. Appliedto
data:
T b F D
n
E
.
consistency:
T b F D
n
E
→ h T
i F
Central
•
limittheorem:
T b F D
n
E
≈∼N h
h T i F , /n V
i
= V E
h IF
; X T, i F
h IF
; X T, i F
T.
66
Modelwith
•
density
h f i x,θ
Maximum
− →
likelihood est.
Moregener
•
al:M-estimators
P ψ
iD X ,
ib θ E
=0
Functional:
ψ R h i x,θ
h dF i x
=0
MLE:
h ψ i x,θ
∂
= log
∂θh h f ii x,θ
s =:
h i x,θ
.
• IFhx;
i F
=
−1
M hx,θ ψ
i
= M
∂
R ψ
∂θhx,θ i h f i x,θ
= dx R −
h ψ i x,θ
sh i x,θ
f
Th i x,θ
dx
67
* 3.5 Robust
Estimators
MultidimensionalLocation. a
f x,µ
f =
0
x
− µ
f h
0i z c =
· exp
D P −
(
j (z
j
)
)/
22 E
,
/c 1 π =(2
m/2
)
M-estimators b
P ψ
i jx
−
iµ
,
=0
Natural choice:
ψ
− x µ
w = h i u
− (x
,
µ) u
=
ik x
−
i 2µk
b µ
= X
w
ih u i
i(x
−
iµ) .X w
ih u i
i= M Z w
k
− x µk
x (
−
i)( µ x
−
i) µ f
T 0x
− µ dx
= Z h w
i u
(
uf
) u
h i u
· du
= I
1
I b
,
68
Sensitivität,Huber-Funktion. c
∗
γ h T, i F
x
=sup hk h IF
x T, ; ik F
i
Censorthe scores
− x
!
µ
− → h w
i u h =min
,c/u 1 i
M-Schätzungenfür d
|
Σ
.
|
b Σ
= X
w
i|
Σ h u i
i(x
−
iµ)(x
−
i Tµ)
.X w
i|
Σ h u i
iu
=(
ix
−
i) µ b
T|
Σ
− 1
x (
−
i) µ
.
Breakdown e
Point.