Random walk smooth transition autoregressive models

This paper extends the family of smooth transition autoregressive (STAR) models by proposing a speci.cation in which the autoregressive parameters follow random walks. The random walks in the parameters capture permanent structural change within a regime switching framework, but in contrast to the time varying STAR (TV-STAR) speci.cation introduced by Lundbergh et al (2003), structural change in our random walk STAR (RW-STAR) setting follows a stochastic process rather than a deterministic function of time. We suggest tests for RW-STAR behaviour and study the performance of RW-STAR models in an empirical setting, focussing on interpretation and out of sample forecast performance.