The gap between high- and low-income groups is the widest it has been in 100 years, and the share of U.S. consumers who identify with the middle class has never been lower. Like other retail sectors, the restaurant industry is feeling the effects of this cultural and economic phenomenon, reports The NPD Group, a leading global information company. One of the effects of income bifurcation is that visits to quick service restaurants, which have an average check size of about $5, were flat in the year ending June 2014 compared to same period last year, and visits to fine dining restaurants, which have an average check size of $40, were up 3 percent. Total restaurant industry traffic was flat for the period. …