Published online by Cambridge University Press: 24 February 2015
In this paper, we propose a simple nonparametric test for testing the null hypothesis of constant coefficients against nonparametric smooth coefficients in a semiparametric varying coefficient model with integrated time series. We establish the asymptotic distributions of the proposed test statistic under both null and alternative hypotheses. Moreover, we derive a central limit theorem for a degenerate second order U-statistic, which contains a mixture of stationary and nonstationary variables and is weighted locally on a stationary variable. This result is of independent interest and useful in other applications. Monte Carlo simulations are conducted to examine the finite sample performance of the proposed test.
We thank the anonymous referees, Peter Phillips and Qiying Wang for their insightful comments that greatly improved our paper. Sun’s research is supported by the Social Sciences and Humanities Research Council of Canada (SSHRC) grant 410-2009-0109. Cai’s research is supported, in part, by the National Nature Science Foundation of China grants #71131008 (Key Project) and #70971113. Li’s research is partially supported by the National Nature Science Foundation of China grant #71133001.