other races. The factors contributing to the wage gaps for various races and the degree to which they affect each race varies, but many factors are common to most or all races. Educational disparities Education being one of the leading determinants of wage, contributes in a similar manner to the racial wage gap. Varying education levels among races lead to different wages for various racial groups. Education affects wages because it allows access to occupations of higher status that offer greater earnings. Mary C. Waters and Karl Eschbach studied the decrease in the black-white wage gap from the 1940s through the 1970s and found the primary reason for the decrease in the wage gap to be the narrowing of the education gap between blacks and whites. Occupational distribution disparities The way in which races are distributed throughout occupations affects the racial wage gap. White and Asian Americans, who have the highest median incomes, are concentrated more in professional, executive, and managerial occupations than blacks, Hispanics, or American Indians. Black and Hispanic workers are not only more likely to work in blue-collar or service jobs, but they tend to be concentrated in the lower-wage/skilled jobs, such as operators, fabricators, and laborers, rather than higher-paying precision production and craft jobs within those categories. Occupational distribution varies for women of various races as well. White and Asian women are more likely to work in managerial and professional occupations, while black, Hispanic, and American Indian Women are more likely to work in service occupations. Thus, because certain races are more likely to have lower-paying jobs, gaps in median incomes between races arise. A study conducted by Kenneth Couch and Mary Daly found that the occupational distribution between blacks and white improved between 1970 and the 1990s. In 1968, a black male was only 20 percent as likely to be employed as a manager as a white male and only 40 percent as likely to work in a professional occupation. In 1998, the percentages increased to 50% and 70 percent, respectively. Despite this improvement, however, occupational distribution differences still exist between blacks and whites. In 1998, a black male was still more likely than a white male to work in lower-skills jobs and less likely than a white male to work in high-paying jobs. Globalization The globalization of the United States' economy in the 1970s and 1980s caused a shift in the U.S. income distribution.