In this article we give a review of regression-based Monte Carlo methods for pricing American options. The methods require in a first step that the generally in continuous time formulated pricing problem is approximated by a problem in discrete time, i.e., the number of exercising times of the considered option is assumed to be finite. Then the problem can be formulated as an optimal stopping problem in discrete time, where the optimal stopping time can be expressed by the aid of so-called continuation values. These continuation values represent the price of the option given that the option is exercised after time t conditioned on the value of the price process at time t. The continuation values can be expressed as regression functions, and regression-based Monte Carlo methods apply regression estimates to data generated by the aid of artificial generated paths of the price process in order to approximate these conditional expectations. In this article we describe various methods and corresponding results for estimation of these regression functions.
Pricing of American options as optimal stopping problemIn many financial contracts it is allowed to exercise the contract early before expiry. E.g., many exchange traded options are of American type and allow the holder any exercise date before expiry, mortgages have often embedded prepayment options such that the mortgage can be amortized or repayed, or life insurance contracts allow often for early surrender. In this article we are interested in pricing of options with early exercise features.It is well-known that in complete and arbitrage free markets the price of a derivative security can be represented as an expected value with respect to the so called martingale measure, see for instance Karatzas and Shreve (1998 There are various possibilities for the choice of the process (X t ) 0≤t≤T . The most simple examples are geometric Brownian motions, as for instance in the celebrated Black-Scholes setting. More general models include stochastic volatility models, jump-diffusion processes or general Levy processes. The model parameters are usually calibrated to observed time series data.The first step in addressing the numerical solution of (1) is to pass from continuous time to discrete time, which means in financial terms to approximate the American option by a so-called Bermudan option. The convergence of the discrete time approximations to the continuous time optimal stopping problem is considered in Lamberton and Pages (1990) for the Markovian case but also in the abstract setting of general stochastic processes.For simplicity we restrict ourselves directly to a discrete time scale and consider exclusively Bermudan options. In analogy to (1), the price of a Bermudan option is the value of the discrete time optimal stopping problemwhere X 0 , X 1 , . . . , X T is now a discrete time stochastic process, f t is the discounted payoff function, i.e., f t (x) = d 0,t g t (x), and T (0, . . . , T ) is the class of all {0, . . . , T }-valued stopping times. He...