Estimates of the discriminatory component of the gender pay gap vary. The OECD estimated that approximately 30% of the gender pay gap across OECD countries is because of discrimination. Australian research shows that discrimination accounts for approximately 60% of the wage differential between men and women. Studies examining the gender pay gap in the United States show that a much of the wage differential remains unexplained, after controlling for factors affecting pay. One study of college graduates found that the portion of the pay gap unexplained after all other factors are taken into account is five percent one year after graduating and 12% a decade after graduation. A study by the American Association of University Women found that women graduates in the United States are paid less than men doing the same work and majoring in the same field. Wage discrimination is theorized as contradicting the economic concept of supply and demand, which states that if a good or service (in this case, labor) is in demand and has value it will find its price in the market. If a worker offered equal value for less pay, supply and demand would indicate a greater demand for lower-paid workers. If a business hired lower-wage workers for the same work, it would lower its costs and enjoy a competitive advantage. According to supply and demand, if women offered equal value demand (and wages) should rise since they offer a better price (lower wages) for their service than men do. Research at Cornell University and elsewhere indicates that mothers in the United States are less likely to be hired than equally qualified fathers and, if hired, receive a lower salary than male applicants with children. The OECD found that "a significant impact of children on women's pay is generally found in the United Kingdom and the United States". Fathers earn $7,500 more, on average, than men without children do. There is research to suggest that the gender wage gap leads to big losses for the economy. According to Denise Venable at the National Center for Policy Analysis, the "wage gap" in the United States is not the result of discrimination but of differences in lifestyle choices. Venable's report found that women are less likely than men to sacrifice personal happiness for increases in income or to choose full-time work. She found that among American adults working between one and thirty-five hours a week, and part-time workers who have never been married, women earn more than men. Venable also found that among people aged 27 to 33 who have never had a child, women's earnings approach 98% of men's and "women who hold positions and have skills and experience similar to those of men face wage disparities of less than 10 percent, and many are within a couple of points".