“…There are multiple ways to handle regime changes, such as with time-varying AR, MA, CL, and CLMA terms to reflect parameter changes (Bringmann et al, 2016), while keeping in mind that this makes a model sensitive to noise (Boldea & Hall, 2013;Perron, 2006;Stock & Watson, 2009). As with trends, there is no magic bullet for regime changes, and their existence is often uncertain (Badagián, Kaiser, & Peña, 2015). Our model can account for some regime changes with an occasion effect a t , a time-varying unit effect l t Z i (and covariance c ðxyÞ Z ), and impulse terms c ðyÞ u t , c ðxÞ u t , and c ðxyÞ u t that are free to vary.…”