In one, Kenneth Stone, a professor of economics at Iowa State University, found that some small towns can lose almost half of their retail trade within ten years of a Walmart store opening.[44] However, in another study, he compared the changes to what small town shops had faced in the past—including the development of the railroads, the advent of the Sears Roebuck catalog, and the arrival of shopping malls—and concluded that shop owners who adapt to changes in the retail market can thrive after Walmart arrives.[44] A later study in collaboration with Mississippi State University showed that there are "both positive and negative impacts on existing stores in the area where the new supercenter locates."[45]