Three cost models of water delivery systems are replicated as alternative specifications of a general form. A dual cost function methodology is followed, usin g firm-specific data and ownership proxies, to trace the effects that numerous technical constraints and variable specifications have on t he relative efficiency of firms by ownership type. Results show that apparent overall efficiency differences reduce to insignificance as s pecification improves. This partly explains why past studies of overa ll efficiency of ownership forms have yielded mixed, and in some inst ances, unreliable results. The partial efficiency results point to fu ture public-private research methods. Copyright 1987 by MIT Press.

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