EXCERPT:
"Serious economists long ago rejected the idea that market structure (the number of competitors in a market) determines whether a market will produce competitive outcomes. Markets with many competitors can nonetheless produce anticompetitive results and markets with few competitors often have vigorous competition (such as Coke and Pepsi). So instead of relying on crude indicators like market structure as a proxy for competition, antitrust economists and regulators require actual evidence of anticompetitive effect.
