Different market structures — common mistakes

When drawing monopoly diagrams, always remember to place the MR curve below the AR (demand) curve, with MR falling at twice the rate of AR. The profit-maximising output is found where MC intersects MR, but the price is read from the AR curve at that quantity.

Comparison essays need two diagrams side by side: PC (horizontal D, P = min AC) vs monopoly (downward D, MR below AR, P > MC). State efficiency implications explicitly for each structure.

No. While the profit outcome is the same, the efficiency is not. In monopolistic competition, the firm produces at a point where price is greater than marginal cost (P>MC), indicating allocative inefficiency. Furthermore, it does not produce at the lowest point on its average cost curve, meaning it is also productively inefficient. This is due to product differentiation giving the firm a downward-sloping demand curve.

Not necessarily. A natural monopoly can be more productively efficient than multiple competing firms due to economies of scale, potentially leading to lower prices if regulated. Also, the supernormal profits earned by a monopoly can be used to fund research and development (R&D), leading to dynamic efficiency and innovative products that benefit consumers in the long run. However, an unregulated profit-maximising monopoly is likely to charge high prices and restrict output.

Due to interdependence, firms are wary of starting a price war. If one firm cuts its price, rivals will likely follow suit immediately to avoid losing market share. The result is that all firms end up with the same market share as before, but at a lower price and with significantly lower profits. Therefore, it is often more rational for oligopolists to maintain price stability and compete on non-price factors like advertising, quality, and service.