“…Examples for such models with partial observation can be found, for instance, in Lakner (1995), Elliott, Lahaie & Madan (1997), Elliott, Fischer & Platen (1999), Babbs & Nowman (1999), Frey & Runggaldier (1999, 2001, Karatzas & Zhao (2001), Pham & Quenez (2001), Nagai & Peng (2002), Bhar, Chiarella & Runggaldier (2004), Haussmann & Sass (2004), Kirch & Runggaldier (2004), Landen (2000), Runggaldier (2004), Gombani, Jaschke & Runggaldier (2005), Cvitanić, Rozovskii & Zaliapin (2006) and Bäuerle & Rieder (2007). For instance, of particular interest are the market prices of risk, which are important hidden quantities that the investors need for portfolio optimization.…”