Non-jointness and scope economies in the multiproduct symmetric generalized McFadden cost function

The multiproduct symmetric generalized McFadden cost function is increasingly prominent in empirical production analysis. Researchers should be aware that the scope for imposing and testing non-jointness in this model is limited. In the general version of the model non-jointness requires the non-testable maintained hypothesis of similar (in a sense we define) single-output production technologies, a maintained hypothesis for which there is not normally any basis. The apparent imposition and testing of non-jointness must be qualified accordingly. The attempt to impose non-jointness and global separability simultaneously necessarily imposes constant returns to scale and the implication that outputs are identical up to a scalar multiple. In this special case the model therefore effectively describes merely the production of a single output, and in this sense is only trivially multiproduct.