Sainsbury’s/Asda and the CMA’s GUPPI decision rule: On the money or basket case?

In April 2019, the UK’s Competition and Markets Authority (CMA) issued one of its highest-profile decisions in recent years, prohibiting the proposed merger between the supermarket chains Sainsbury’s and Asda. In so doing, it relied solely on Gross Upward Pricing Pressure Index (GUPPI) calculations to determine if local overlaps in the parties’ grocery stores were likely to result in a substantial lessening of competition (SLC).

This Brief considers the wider implications of the CMA’s mechanical use of GUPPI values as a decision rule in this case.