The brewing industry has constituted a focus of interest in industrial organization economics since World War II, due to its rapidly increasing concentration, possibly large plant-level scale economies, and marked product differentiation accompanied by relatively high firm advertising intensities. Scherer [ 19, p. 1 10] wrote concerning the dramatic postwar structural change which has characterized this industry:
 ".... That in turn permitted them (Anheuser-Busch, Schlitz, and Pabst) to build additional new breweries which, by exploiting a combination of technological advances and scale-up economies, had much lower production costs per unit than those of regional brewers lacking premium image brands.. With lower costs, the Big Three (joined by Coors and later Miller's) could squeeze the premium-popular price differential, enhancing their market shares even more, which in turn permitted them to advertise as heavily in absolute terms as smaller regional rivals but at appreciably lower average outlays per sales dollar. The upshot of these interacting developments was an increase in the four-firm concentration ratioinbrewingfrom21 in 1947 to61 in 1976."