A Consistent Nonparametric Test for Causality in Quantile



used as a proper candidate for consistent testing H0 (Li, 1999, p. 104). Since

Е(^, I zt ) = Fyz {Qθ (xt ) I zt }- θ , we have

J = E {εt E(εtzt ) fz (zt )}.

(6)


The test is based on a sample analog of E{ε E(ε z) fz(z)}. Including the density

function fz (z) is to avoid the problem of trimming on the boundary of the density function,
see Powell, Stock, and Stoker (1989) for an analogue approach. The density weighted
conditional expectation
E(ε z) fz(z) can be estimated by kernel methods

E(£t I zt )fz ( zt ) =


---i---Σ Ks'
-1) h ~ ts


(7)


where m=p+q is the dimension of z , Kts= K {(zt -zs)/h} is the kernel function and

h is a bandwidth. Then we have a sample analog of J as

1 TT

T ≡--------∑ ∑ Ksεtεs

Tm         tsts

T(T- 1)h  t=1  st

1 TT

t,t 1,h∑ ∑ K [I{У, Q(x)}-θ][I{у.Qθ(χ.)}-θ]    (8)

T(T- 1)h t=1 st

The θ-th conditional quantile of yt given xt, Qθ (xt ), can also be estimated by the
nonparametric kernel method

( χt ) = Fyx ^1(θxt ),
where

(9)


(10)


L.I (У. У. )
λ

F7yx(yt I xt ) = ^≠^ντ7------

Lt.

.t

is the Nadaraya-Watson kernel estimator of Fyx (yt xt) with the kernel function of

[x4 - x I                                       _

------I and the bandwidth parameter of a . The unknown error ε can be
a J

estimated as:



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