Further application of the methodology used by Card and Krueger by other researchers yielded results similar to their original findings, across additional data sets. A 2010 study by three economists (Arindrajit Dube of the University of Massachusetts Amherst, William Lester of the University of North Carolina at Chapel Hill, and Michael Reich of the University of California, Berkeley), compared adjacent counties in different states where the minimum wage had been raised in one of the states. They analyzed employment trends for several categories of low-wage workers from 1990 to 2006 and found that increases in minimum wages had no negative effects on low-wage employment and successfully increased the income of workers in food services and retail employment, as well as the narrower category of workers in restaurants.