About one-third of U.S. women\'s wage gains during the 1990s were due to the availability of oral contraceptives, researchers found. Martha Bailey and Brad Hershbein at the University of Michigan, and Amalia Miller at the University of Virginia, said although women lag behind men in wages, the gender wage gap has narrowed considerably since the 1960s. Bailey and colleagues, using the National Longitudinal Survey of Young Women, analyzed the careers of approximately 4,300 women born from 1943 to 1954. The women varied in their legal ability to obtain the pill from their doctors between the ages of 18-21. \"We found that women who had early access to the pill in the 1960s and 1970s earned 8 percent more on average by the 1980s and 1990s than women without early access,\" Bailey said in a statement. After the U.S. government approved the pill in 1960, laws in different states placed different age limits on women obtaining the oral contraceptive. As the voting age dropped to 18, the law for women to obtain the pill eased as well, so women no longer had to choose between looking for a mate -- and the risk of pregnancy -- and investing in their educations and careers, because they could do both, researchers said. \"As the pill provided younger women the expectation of greater control over childbearing, women invested more in their human capital and careers,\" Bailey said. \"Most affected were women with some college, who benefited from these investments through remarkable wage gains over their lifetimes.\" The study, published by the National Bureau of Economic Research as a working paper, is scheduled to be published in July in the American Economic Journal: Applied Economics.