The latest war on abortion is being fought less over women's bodies than over their minds. In the past few years, under the banner of "a woman's right to know," a number of states have passed laws mandating that women seeking abortions be told that going ahead with the procedure would expose them to mental health risks, including post-traumatic stress and a greater danger of suicide.

Such warnings might sound like a good idea. The decision to terminate a pregnancy can be difficult, and some women end up regretting it. It's commendable to help women make an informed choice. But an informed choice requires accurate information. And these laws mandate that women be misled.

Rigorous U.S. scientific studies have not substantiated the claim that abortion, compared with its alternatives, causes an increased incidence of mental health problems. The same conclusion was reached in 2008 by an American Psychological Association task force, which I chaired, as well as by an independent team of scholars at Johns Hopkins University. As recently as September, Oregon State University researchers announced the results of a national study showing that teenagers who have an abortion are no more likely to become depressed or to have low self-esteem one year or five years later, compared with their peers who deliver.

Even so, the claim that abortion harms women's mental health persists. According to research by the Guttmacher Institute, counseling on the negative psychological effects of abortion is mandatory in Mississippi, Nebraska, South Carolina, South Dakota, Texas, Utah and West Virginia. Promoting this claim is part of a political strategy aimed at dissuading women from terminating a pregnancy and at making abortions difficult, if not impossible, to obtain. It is a strategy that distorts scientific principles, even as it uses the umbrella of scientific research to advance its aims.

As part of this strategy, some antiabortion activists, such as David Reardon of the Elliot Institute, an antiabortion advocacy group, have scoured existing survey data for evidence linking abortion and a wide variety of mental health issues, such as depression, anxiety and alcohol use. They cite any correlations they find as evidence that abortion causes harm to women.

But there are at least two logical flaws at play here. The first is a confusion of correlation with causation. The most plausible explanation for the association that some studies find between abortion and mental health is that it reflects preexisting differences between women who continue a pregnancy and those who end one.

A substantial amount of research shows that women who deliver babies are, on average, more likely to have planned and wanted their pregnancies and to feel emotionally and financially capable of becoming a mother. In contrast, women who seek abortions are, on average, less likely to be married or involved in an intimate relationship, more likely to be poor, and more likely to have suffered physical or psychological abuse. All of these latter qualities are risk factors for poor mental health.

State lawmakers in Nebraska willfully ignored the difference between correlation and causation in April, when they passed a law requiring that health-care providers inform women seeking abortions if they have any characteristics - such as being poor or having low self-esteem - shown to be related to mental health problems following an abortion. If a woman experiences certain difficulties after an abortion, she can file a civil lawsuit against her physician claiming that she wasn't screened adequately for those characteristics. It's an option sure to discourage doctors from offering the procedure, if they aren't already disinclined.

The law ignores the fact that the very characteristics that predispose women to emotional or mental health problems following an abortion also predispose them to postpartum depression if they deliver or to mental health problems in general, even if they do not become pregnant.

Following the logic of this purportedly protective law, women wanting to deliver a child should likewise be screened to ascertain that they are not predisposed to poor mental health afterward.

A second logical failing in the campaign to convince women that abortion harms their mental health involves what psychologists call the "availability heuristic." Essentially, it means that vivid, first-person accounts that can be easily brought to mind, such as the personal stories of women who feel harmed by abortion, influence our estimates of the frequency of an event more than dry, statistical data do. For example, people think the probability of dying by homicide is greater than that of dying by stomach cancer, even though the rate of death by the latter is five times higher than death by the former. They err because examples of homicide are easier to recall than examples of stomach cancer.

In just this way, the emotionally evocative stories of a minority of women can lead people to overestimate the frequency of those experiences. For example, one woman who shared her story on an antiabortion Web site said that after her abortion, "I became very depressed and tried to kill myself by taking an entire bottle of pain pills, and I was unconscious for three days." Her story drowns out the evidence that a much larger number of women feel relief following an abortion.

My research, based on clinic interviews in the 1990s with more than 400 women who obtained a first-trimester abortion, shows that women who terminate an unplanned pregnancy report a range of feelings, including sadness and loss as well as relief. Nonetheless, two years after their abortion, most women say they would make the same decision if they had it to do over again under the same circumstances. Because of the stigma attached to abortion in our society, however, most women feel they can't talk about their abortions - unless they repent.

Women who think they made the right decision in having an abortion must be able to say so without fear of condemnation and without feeling that something is wrong with them. And women who feel sadness and regret should feel free to share their feelings as well. But their words should not be used to deceive women or to limit their choices.

Brenda Major is a professor of psychology at the University of California at Santa Barbara and a fellow at the Center for Advanced Study in the Behavioral Sciences at Stanford University.