The mean-variance model is precisely consistent with the expected utility hypothesis only in the special cases of normally distributed security returns or quadratic utility functions. There is little evidence, however, that security returns follow normal distributions (see [13] for references) and quadratic preferences can be shown to generate implausible results, exhibiting increasing absolute risk aversion in the Pratt [ll]–Arrow [1, 2] sense and displaying negative marginal utility after some finite wealth level. In addition, Hakansson [4] has shown that single–period, mean-variance-efficient portfolios can have disastrous consequences over time—even when return distributions are stationary. Such criticisms of the mean-variance approach within the Von Neumann-Morgenstern framework have prompted several writers to suggest that investors maximize the expected value of utility functions with more “realistic” properties, while others have criticized the single-period focus of the model. One popular alternative utility function is the logarithmic function which exhibits decreasing absolute risk aversion and (conveniently) leads to myopic decision processes through time (i.e., investors treat each period as if it were the last, basing investment decisions on that period's wealth and return distributions only [8, 4]). (Other utility functions with constant relative risk aversion—such as the power function—also imply myopic decision rules within a multiperiod setting.)

The composite cost function the authors propose combines a quadratic output structure with a log-quadratic input price structure and is well suited for examining economies of scope, subadditivity, and other important properties of multiproduct firms. To compare the composite model with an appropriate set of alternative functional forms, they develop a parsimonious--but general--specification that nests the standard translog cost function, the generalized translog cost function, a separable quadratic cost function, and the composite cost function. An application to economies of scope in banking confirms the advantages of the composite model. Copyright 1992 by MIT Press.

In providing financial services jointly, banks may reduce costs due to complementarities in production (cost economies of scope) or raise revenues from complementarities in consumption (revenue economies of scope). Cost economies of scope between bank deposits and loans have been found to be small. Revenue economies of scope are investigated here for the first time and found to be insignificant over 1978–1990 for both small and large banks and for those on or off the revenue-efficient frontier. The lack of complementarities between deposits and loans — where benefits are most likely to occur — suggests that claims of important synergies from an expansion of banking powers be taken with caution.

Virginia State Corporation Commission