“…The problem is that specific numerical values of the underlying parameters give rise to the same term structure. See for instance,Dai and Singleton (2002),Duffee (2002),Dai and Philippon (2005),Kim and Orphanides (2005),Kim and Wright (2005),Lemke (2006), Bolder (2006,), D'Amico et al (2008b), Pericoli and Taboga (2008 andAdrian and Wu (2009). show that if one restricts a specific set of parameters, this allows to treat the more "interesting" parameters to the econometrician as free parameters.…”