Presents a reply to Vickrey's comment on the study on the additivity of current cash equivalent. Rejection of the possibility that CCE could be defined as numerosity; Argument that purchasing power is nonadditive; Recommendations for future research.

[In this paper we analyze implications of a singular contemporaneous disturbance covariance matrix for the estimation and hypothesis testing of systems of equations with autoregressive disturbances. We find that this singularity imposes restrictions on the parameters of the autoregressive process. When these restrictions are not imposed, the specification, maximum likelihood estimates, and likelihood ratio test statistics are conditional on the equation deleted. Furthermore, singularity of the contemporaneous disturbance covariance matrix raises issues concerning identification of parameters of the autoregressive process. This identification problem complicates the interpretation of likelihood ratio statistics. The above results are illustrated with an empirical example.]

Industrial demand for energy is essentially a derived demand: the firm's demand for energy is an input is derived from demand for the firm's output. Inputs other than energy typically also enter the firm's production process. Since firms tend to choose that bundle of inputs which minimized the total cost of producing a giving level of output, the derived demand for inputs, including energy, depends on the level of output, the submitions possibilies among inputs allow by production technology, and the relative prices of all inputs.

Gail R. Wilensky, Wayne Vroman, The Social Security Payroll Tax: Some Alternatives for Reform: Discussion, The Journal of Finance, Vol. 30, No. 2, Papers and Proceedings of the Thirty-Third Annual Meeting of the American Finance Association, San Francisco, California, December 28-30, 1974 (May, 1975), pp. 579-584