1. A method for determining price, f(S), of a derivative having an underlying financial instrument, said method including the steps of: (a) determining a non-Gaussian model of price, S, of the underlying financial instrument, said model assuming statistical feedback, where the price S is S=S(t+τ)=S(τ)e Y(t) , where t denotes a time delay, time interval, or timescale, τ is an initial time value, τ=0 without loss of generality, Y(t) is a value that evolves across timescale t, and the underlying financial instrument has a return; and (b) by operating a computer system, determining as price f, a derivative price value consistent with the model determined in step (a), including by generating data indicative of the derivative price value.