Similarly, a comprehensive study by the staff of the U.S. Government Accountability Office found that the gender wage gap can only be partially explained by human capital factors and "work patterns." The GAO study, released in 2003, was based on data from 1983 through 2000 from a representative sample of Americans between the ages of 25 and 65. The researchers controlled for "work patterns," including years of work experience, education, and hours of work per year, as well as differences in industry, occupation, race, marital status, and job tenure. With controls for these variables in place, the data showed that women earned, on average, 20% less than men during the entire period 1983 to 2000. In a subsequent study, GAO found that the Equal Employment Opportunity Commission and the Department of Labor "should better monitor their performance in enforcing anti-discrimination laws."