Chicago, IL -- One in six Americans report being responsible for a pregnancy that ended in abortion, according to University of Chicago researchers who on Wednesday released more data from the National Health and Social Life Survey, regarded by experts as the nation's most comprehensive scientific study of American sexual behavior and attitudes.

"Sex, Love, and Health: Private Choices and Public Policies," composed of reports by 16 researchers, is the second installment of the U. of C. project launched a decade ago by the National Institutes of Health to update a body of research on sex that hadn't changed much since the Kinsey reports of the 1940s and 1950s.

"We view sexual practices as an ongoing series of interactions whose content, pacing and partner choice are based not only on the character of the relationship between the people involved, but also on the social networks in which they live," said Edward O. Laumann, one of two lead researchers on the project.

The other lead researcher, Robert T. Michael, noted: "Because of the public consequences of these private acts, our society faces the need to create public policies to address these issues."

Laumann is a professor and formerly chairman of the Department of Sociology and provost at the University of Chicago; Michael is a professor and dean of the university's Harris Graduate School of Public Policy.

Researchers and advocacy groups have never agreed on a host of statistics about abortion, and this study offers a yet new set of numbers.

The U. of C. researchers found that a first pregnancy (especially if it occurred in the teen years) and late pregnancies (especially in the mid-30s and older) are the ones most likely to be aborted, with pregnancies in the 20s and early 30s more likely to go to term.

A teenage girl is much more apt to have an abortion if her parents are better educated and less likely if she is African-American, though black women have on average more conceptions and are more likely to have had an abortion over their lifetime.

Although opinions about abortion appear to influence choice, marital status and a mother's career opportunities play an important, independent role. And those who abort one pregnancy are more likely to abort a second, even though the vast majority of women who undergo an abortion during their reproductive years have only one.