applying a change of variable from (xi,xj) = (xi,u) where u = xj-xi we get the following expression
1 C KK2(u) + £hRK(u)g(xi + hu)du∖2 — 2K(u) £hRK(u)g(xi + hu)du∖
= 4hJ J ---------------------------g2χ)---------------------------g(Xi)g(xi + hu)du '
' 41h K K2(u)du + o( 1) = O(1).
4h h h
(61)
Similarly we can show that
E [Jn(xi,xj)Jn(xj ,xi)]
' 4-h( K2(u)du + o(h) = O(h).
4h h h
(62)
Then it follows that
and
E H12n (xi
xj)∖ = E £2Jn (xi,xj)+ Jn (xi,xj)Jn (xj ,xi
)1 = h/
K 2(u)du + o(ɪ) = θ(ɪ),
hh
(63)
21
σ2n = n2h J K2(u)du + o(h).
(64)
The second term in () is the expected value of a Bias term, that is
Bbn 1 X bn(xi) ' h-μ2 I g(2∖x')dx + o(h2),
n2
i
(65)
where g(2)(x) is the second derivative of the p.d.f. Hence Bbn = Op (n 1/2h2^ Thus, what we obtain is
^ ^ ^
V1n = V11n + Bn
σ1nN(0, 1) + y μ2
g(2)(x)dx+o(h2).
(66)
1
V2n = —
n
i
"p"" / ∖ P/ ∖
fn(xi) — f(xi)
g(xi)
— "I 2
+ f (xi) - g(xi)
g(χi)
“ --—~~ ___
fn(xi) — f (xi)
g(xi)
f (xi) — g(χi)
g(χi)
f fn(xi) — f (xi)
∖ g(xi)

(67)
= Vb21n + Vb22n + Vb23n. (68)
V21n = 1 X
n
i
2
—1— X an(xi,Xj) I
n—1
j,i6=j
1
n(n — 1)2
ΣΣаП (xi,xj )+ ( ⅛π∑ ∑∑αn(xi>Xj )αn(xi,xz ).
n(n — 1)
i j,i6=j i j6=i z6=j
(69)
The first part is a variance term and it will affect the mean of the asymptotic distribution. The second
term equals a twice centered degenerate U-statistic U2n, which is of the same order of magnitude of V11n
and it also affects the asymptotic distribution of KI.
27
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