How useful are the models of market structure?

Overview

Monopolistic competition model fail to capture about real differentiated markets and two firms with the same market share behave completely differently.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Why is the perfectly competitive model worth studying when almost no real market satisfies its assumptions?

   Model answer

   It works as a benchmark rather than a description. Because it produces a determinate outcome in which price equals marginal cost and equals minimum average total cost, it defines what an efficient market would look like, and every other structure can be measured against that standard. It also isolates the mechanism, showing precisely how free entry converts supernormal profit into lower prices, which is the reasoning applied to real markets where entry is merely easy rather than perfectly free. A model is judged by whether its predictions are useful, not by whether its assumptions are literally true.

2. 2

   Which of the assumptions of perfect competition is least realistic, and what difference does relaxing it make?

   Model answer

   Perfect information is the hardest to defend, since real buyers face search costs and cannot compare every seller, and real firms do not know rivals' techniques. Relaxing it gives every firm a pocket of price-setting power, because some customers will not discover the cheaper alternative, so the firm's demand curve slopes downwards instead of being horizontal. Price then exceeds marginal cost, identical products can sell at different prices in the same market, and advertising becomes worthwhile. The market comes to resemble monopolistic competition, which is why that model describes so many real markets.

3. 3

   Which real markets come closest to perfect competition, and in what respects do they still fall short?

   Model answer

   Markets in standardised commodities come closest: foreign exchange, wholesale electricity, and agricultural products such as wheat, where the product is near-identical, there are many buyers and sellers, and prices are published continuously. They still fall short in several ways. Entry into farming requires land and capital, which is a real barrier. Government intervention alters prices and output. Transport costs mean location matters, so the product is not truly identical. And in electricity a handful of large generators can affect the price at peak times, which no true price taker could do.

4. 4

   Why does the monopolistic competition model describe more real markets than either perfect competition or monopoly?

   Model answer

   Its assumptions match what is commonly observed: many small firms, an easily entered trade, and products that are similar but not identical. Hairdressing, plumbing, independent cafés, takeaways and local building firms all fit, since each has a few loyal customers who will pay a little more for their preferred supplier while none has real power over the market. The model also explains features the other two cannot, notably why firms advertise and why they carry spare capacity. Branding is rational rather than pointless in this model, as it also is in oligopoly, whereas perfect competition and pure monopoly leave no role for it.

5. 5

   What does the monopolistic competition model fail to capture about real differentiated markets?

   Model answer

   It assumes firms ignore each other, which is untrue once a market contains a few large brands whose promotions are aimed at specific rivals. It treats products as differentiated but comparable, whereas real differentiation can be so strong that separate markets exist. It assumes free entry, ignoring the sunk cost of building a brand, which is exactly what makes an established name hard to displace. It also has no account of how firms choose how much to differentiate, treating the product as given when in practice that choice is the main decision the firm makes.

6. 6

   Analyse the strengths of the monopoly model as a description of real firms with market power.

   Model answer

   It correctly predicts the central behaviour: a firm that faces a downward-sloping demand curve restricts output below the level at which price equals marginal cost, and the more inelastic the demand the larger the mark-up. That prediction holds whether the firm is a sole supplier or merely a dominant one, so the model illuminates far more markets than pure monopoly. It also explains why such firms invest in protecting their position, and it gives a clear framework for judging when intervention could raise welfare.

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