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Competition and Market Power

Concentration ratios, interdependence and tacit agreement

  • 3 things to know
  • Papers 1 and 3

Overview

Concentration ratios and calculating them and market share, interpreting a high ratio and its weaknesses, interdependence in oligopoly, reluctance to cut or raise price, the kinked demand curve, price wars, tacit collusion and why regulators struggle to prove it, and the incentive to cheat on collusion.

What you need to know

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Key term

How is the dominance of a few firms measured, and how do those firms then behave towards one another?

Key term

What does a concentration ratio measure?

Numbers

Four firms hold 22%, 18%, 15% and 9% of a market. Calculate the four-firm concentration ratio.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What does a concentration ratio measure?

    Model answer

    A concentration ratio measures the combined market share held by the largest few firms in a market.

  2. 2

    Four firms hold 22%, 18%, 15% and 9% of a market. Calculate the four-firm concentration ratio.

    Model answer

    The four-firm concentration ratio is 64%.

  3. 3

    The three largest firms in a market hold 30%, 25% and 12% of sales. Calculate the three-firm concentration ratio and the share left to all other firms.

    Model answer

    The three-firm concentration ratio is 67% and the remaining firms share the other 33%.

  4. 4

    What does a five-firm concentration ratio of 90% tell you about a market?

    Model answer

    The market is highly concentrated and is an oligopoly, because five firms make almost all of the sales.

  5. 5

    State one weakness of the concentration ratio as a measure of competition.

    Model answer

    It counts market share but not the threat of entry, so a concentrated market that is easy to enter may still be competitive.

  6. 6

    A firm sells £24 million in a market worth £160 million in total. Calculate its market share.

    Model answer

    Its market share is 15%.

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