We propose two nonparametric transition density-based speciÞcation tests for continuous-time diffusion models. In contrast to marginal density as used in the literature, transition density can capture the full dynamics of a diffusion process, and in particular, can distinguish processes with...

Time-varying coefficient models have been widely used to model changing relationships of economic and financial variables. The existing literature usually specifies the time-varying coefficient vector as a stochastic stationary process, a deterministic function of time, or a unit root process....