In this context it is worth noting that some securities firms such as Merrill, Lynch. Pierce, Fenner and Smith regularly publish a "beta book in which they report estimates of a and Beta based on standard OLS regression methods, as well as "adjusted Beta"estimates that attempt to deal with the zero Beta portfolio problem mentioned above, using more complex Bayesian statistical procedures. Although these Bayesian procedures are of considerable interest, they are beyond the scope of this chapter.