Could two of the big four companies in an industry merge and actually spur competition, expansion and lower prices for consumers?  

That’s what Sprint and T-Mobile say they hope will happen if they can receive approval to merge, and they could well be right. They face a tough challenge. The Herfindahl-Hirschman index measures market concentration on a 1-10,000 scale – an industry with one company would receive a score of 10,000; one with thousands of competitors would be close to zero.