New research has found that the early availability of the birth control pill is responsible for about a third of women’s wage increases relative to men since the 1960’s, Live Science reports.

Birth control pills. (AP )

“As the pill provided younger women the expectation of greater control over childbearing, women invested more in their human capital and careers,” study researcher and University of Michigan economist Martha Bailey said in a statement, according to Live Science.

Using data from a longitudinal study of women, Bailey and her colleagues found that there was a crucial difference for women who lived in states where women could get the pill without parental permission at age 18, and states where the age was 21.

Women in early-access states, researchers said, no longer had to choose at 18 between investing in their career or investing in a husband. They could do both, without the fear of pregnancy.

The pill has long been hailed as both an accomplishment in public health and agent of change for women — allowing them to choose if and when they would have children.

By the 1980s and 90s, the women who had early access to the pill were making 8 percent more each year than those who didn’t, according to the study.

Bailey said the study also likely underestimated the role of the pill for women’s wages, as researchers did not measure its effect after age 20.

However, the historical benefit to women’s wages may not have much of an impact on changing the viewpoint of women today, Slate XX Factor blogger J. Bryan Lowder suggests.

Lowder cites a Politico piece that found GOP presidential candidate Rick Santorum was surging in popularity among conservative women — in large part because he has promised to help make it possible for women to stay at home with children if they want to.