Alternative representation of the deadweight loss triangle in oligopoly
Authors: Özçam Ahmet 
Published: June 2017

Purpose
The purpose of this paper is to provide an alternative way of calculating the deadweight loss triangle in oligopolistic markets which takes inefficient use of inputs into account. The author shows that the result of the approach coincides with the one that exists in the economics literature. However, the author explicitly accounts for the inefficient use of inputs.

Design/methodology/approach
The market supply curve that is extensively used for competitive markets has been reconsidered for the imperfectly competitive markets. The necessary condition for the efficient use of resources is investigated and a price level is derived at which the market output of oligopoly is produced efficiently. The degree of inefficient use of inputs is reported via the definitions of Input Inefficiency Measure (IIM) and the Ratio of Inefficient usage of Inputs to Total Deadweight Loss (RITD).

Findings
The author discovers that the area under the supply curve of the competitive market corresponds precisely to the minimum total costs of producing any given market output. To make this important finding operational in imperfectly competitive markets, the IIM reports the degree of distorted input allocation among firms with differentiated cost structures in producing a given equilibrium imperfectly competitive market output. In measuring the monopoly power, it is known that CRn or HHI market concentration indexes, which are calculated based on the market shares of firms regarding the demand side of the market, are widely used. The measures, which take into account of the distortions in input usage, and hence, the supply side may be considered as an additional index. For example, if the market demand were shared equally by two firms (no dominant firm with respect to the demand side), it is known that the leadership would still arise when the costs of firms differed as in the dominant firm model in favor of the lower cost producing firm.

Research limitations/implications
The author recommends some more theoretical research extensions of the approach suggested here to other oligopolistic markets like the Cournot-Nash, the Stackelberg and other models. In all cases, there is a need for additional work to find some measurable variables in practice in order to estimate the input inefficiency given by the two measures and differentiate it from the inefficiency of units of outputs that are not produced.

Practical implications
It may be interesting to decompose the various estimates of welfare losses due to monopoly power as a percentage of GNP that were discussed in the literature into two inefficiency components: units of outputs that are not produced and units of inputs that are misallocated among firms.

Social implications
The government officials might be interested in assessing the degree of loss of input usage by firms in addition to output loss in oligopolistic markets summarized by the two inefficiency indexes. Law economists may be inspired in discussing the issue of input inefficiency in the context of on antitrust policy.

Originality/value
The author emphasized that the area under the market supply curve minimized the aggregate cost of producing a given total market output in competitive markets. Having recognized the importance of this finding, the author tried to apply it to imperfectly competitive markets and especially to the calculation of deadweight loss in such markets. The author showed that the total social cost could be calculated by including the input inefficiency which can be defined as the extra cost to society arising from not using the most appropriate economic resource allocation among firms in addition to the usual deadweight loss triangle. Moreover, the author had to introduce some more new terms like the market supply curve allocation, the adjusted competitive price, efficiency gain and so on, as they were necessary along the course of the analysis.