This article analyses the stochastic discount factor (SDF) both from the equilibrium perspective, where it appears as a marginal rate of substitution, and from the arbitrage perspective, where it appears as the Radon – Nikodym derivative which allows for a change in the probability measurable space. Its study entails the use of a power utility function, deriving the marginal rate of substitution and the application of the model to Colombian time series. As a result, we confirm the existence of the equity premium puzzle.