I'm reading about stochastic volatility models - the ones which resulted after Wiggins proposed in 1986/7 that $\sigma$ in Black-Scholes should be a stochastic process rather than a constant.
In particular, I am looking at 3 models:
- Hull & White
- Stein & Stein
The book says, after introducing the last one (Heston), that it is an incomplete market because the model has 2 Brownian motions but we only have one risk asset for replication. What I don't understand is, whether this statement about the market completeness relates to just the last model or all 3. To me, they all seem to be incomplete markets.