Is the concentration ratio an accurate measure of the extent of competition? Part 4 The four-firm concentration ratio Part 5 A. is accurate because it is based on estimates from the U.S. Census Bureau. B. is flawed in that it includes sales in the U.S. by foreign firmsincludes sales in the U.S. by foreign firms. C. is flawed in that it does not measure competition between industriesdoes not measure competition between industries. D. is accurate because it is based on national and global competition. E. is flawed in that it is calculated for local markets even though competition in some industries is nationalis calculated for local markets even though competition in some industries is national