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This essay provides an expository survey of that branch of the theoretical literature on product quality determination which assumes that quality can be represented by a scalar. The bulk of the work discussed associates that scalar with durability. Peter Swan's result that market structure has no impact on quality is derived in a straightforward way, and the assumptions on which it rests are identified and discussed. The consequences of relaxing these assumptions, as revealed by the subsequent literature, are described. The general implications of the durability literature are summarized.
Richard Schmalensee (Sun,) studied this question.