In empirical studies of the CAPM, it is commonly assumed that, (a) the return to the value-weighted portfolio of all stocks is a reasonable proxy for the return on the market portfolio of all assets in the economy, and (b) betas of assets remain constant over time. Under these assumptions, Fama...

The stochastic discount factor (SDF) method provides a unified general framework for econometric analysis of asset pricing models. It has recently been pointed out that the generality of the SDF method may come at the cost of estimation efficiency. We show that there is no need for this concern....