Principles of Microeconomics / Unit 10 MIC 0912 review, 2 to 3 minutes
One Merger, Start to Finish
The idea
A single proposed merger carried from the share table to the regulator's decision shows how the antitrust tools fit together. Begin with the market as the merging firms describe it. Compute the four-firm ratio and the Herfindahl-Hirschman Index before the merger, then combine the two shares and recompute; the increase is twice the product of the merging shares. Compare with the agencies' thresholds: a post-merger index above one thousand eight hundred with an increase above one hundred is presumed to lessen competition, as is a merged share above thirty percent with that increase. Next, question the market. If the product competes nationally rather than regionally, or online as well as in stores, every share shrinks and the same merger may clear the thresholds; this is argued first, because it decides the rest. Then look at actual competition: where the two firms overlap, do prices fall, and would they rise if one left? Then weigh the efficiency claim: a merger that lowers average cost through scale can benefit consumers if enough of the saving is passed on, and the regulator sets that against the lost rivalry. The decision is one of three: allow, block, or allow on conditions, usually divestiture of the plants or brands where the overlap is worst, bringing the increase below the threshold and keeping the scale gains elsewhere.
In practice
Worked example: the regional cement market's shares are twenty-five, twenty, fifteen, twelve, ten, eight, six and four. The third and fourth firms propose to merge. Before: ratio seventy-two, index one thousand six hundred ten. After: ratio eighty-two, index one thousand nine hundred seventy, an increase of three hundred sixty; above one thousand eight hundred and above one hundred, so the presumption is tripped. The firms reply that cement ships across three states, where their shares are eight and six: an increase of ninety-six, tripping nothing. Price data show that where the two firms' plants overlap, prices run ten percent below where only one operates. The agency rejects the wider market, credits the overlap evidence, and allows the merger on condition that the overlapping plants, seven points of share, are sold to a new entrant: the merged firm holds twenty, the index is one thousand six hundred ninety, and the increase is eighty.
Where people slip
Three cautions. The thresholds create a presumption, not a verdict; both sides bring market-definition and efficiency evidence. The efficiency defense cuts both ways: scale that lowers cost is real, and so is the market power that comes with it. And the thresholds are the agencies' as of December twenty twenty-three; an exam question may state older ones, so compute the level and the increase and apply the thresholds given.
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