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Limits and Uses of Price Tests for Market Definition


  • Willem H. Boshoff

    () (Department of Economics, University of Stellenbosch)


Various quantitative tools have been developed for defining markets in competition law investigations. Econometric tests on price co-movement represent one such set of tools: two regions or products are considered part of the same market if their prices co-move. However, price co-movement tests, especially the more advanced econometric tests, have been criticized in the competition policy literature. Critics claim that price tests focus only on price linkages and, furthermore, that some of the advanced price tests are misleading in small samples. This paper applies a range of price tests, including correlation analysis, Granger-causality tests, unit root tests and the recent autoregressive distributed lag (ARDL) bounds test, to data from the 2006-2008 competition investigation into business practices in the South African dairy industry. We argue that the different price tests ask different questions and that it is not useful to dismiss an advanced price test if it suggests a different market than that identified by a simple correlation statistic. We also consider the criticism of poor small-sample performance of price tests: many conventional tests have long been shown to suffer from small-sample power and size problems, but critics fail to account for recent improvements in this regard. The paper concludes that the combination of various price-test results offers a rich picture useful for market definition purposes, especially if they are employed as exploratory tools rather than confirmatory ones.

Suggested Citation

  • Willem H. Boshoff, 2011. "Limits and Uses of Price Tests for Market Definition," Working Papers 01/2011, Stellenbosch University, Department of Economics, revised 2013.
  • Handle: RePEc:sza:wpaper:wpapers129

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    File Function: Revised version (version 2), 2013
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    More about this item


    market definition; price correlation; unit root; bounds test; law of one price;

    JEL classification:

    • L40 - Industrial Organization - - Antitrust Issues and Policies - - - General
    • L11 - Industrial Organization - - Market Structure, Firm Strategy, and Market Performance - - - Production, Pricing, and Market Structure; Size Distribution of Firms
    • C32 - Mathematical and Quantitative Methods - - Multiple or Simultaneous Equation Models; Multiple Variables - - - Time-Series Models; Dynamic Quantile Regressions; Dynamic Treatment Effect Models; Diffusion Processes; State Space Models
    • D4 - Microeconomics - - Market Structure, Pricing, and Design

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