Two peer-reviewed articles published Sunday in a scholarly journal cast doubt on a core assumption used to advance same-sex marriage.

A number of studies and articles have suggested that research shows no difference in outcomes between children whose parents have same-sex relationships and their peers raised by heterosexual parents. For example, the American Psychological Association (APA) stated in 2005 that “Not a single study has found children of lesbian or gay parents to be disadvantaged in any significant respect relative to children of heterosexual parents.”

Yesterday the academic journal Social Science Research published a detailed methodological review of the research on which the APA bases its conclusion—a study that questions the validity of the “no difference” assertion. Conducted by a Louisiana State University family scholar, the article concludes:

[N]ot one of the 59 studies referenced in the 2005 APA Brief compares a large, random, representative sample of lesbian or gay parents and their children with a large, random, representative sample of married parents and their children. The available data, which are drawn primarily from small convenience samples, are insufficient to support a strong generalizable claim either way. Such a statement would not be grounded in science. To make a generalizable claim, representative, large-sample studies are needed—many of them.

A large representative sample is supplied in a second new study, conducted by a University of Texas–Austin sociologist and published in the same journal. The New Family Structures Study (NFSS), under the direction of Dr. Mark Regnerus, provides the most representative picture to date of young adults whose parents had same-sex relationships. NFSS is a large, random, nationally representative sample.

In other words, because of how the sample was collected, it is representative of all young adults in this age group in the United States. Knowledge Networks, a respected research firm responsible for collecting the data, screened more than 15,000 young adults (ages 18–39) to identify nearly 3,000 participants, including 175 respondents who reported that their mothers have had a romantic same-sex relationship and 73 respondents who reported that their fathershave. This is the second-largest such sample of children whose parents had same-sex relationships, after the Census. The Census, however, provides a limited set of social welfare outcomes, while NFSS provides data on 40 outcome areas compared across seven family structures.

As Professor Paul Amato of Penn State University notes in his critique of the study, published in the same issue, “The New Family Structures Study is probably the best that we can hope for, at least in the near future.”

According to NFSS, just 1.7 percent of young adults ages 18 to 39 reported having a parent who has had a same-sex romantic relationship. The experience of long-term stability in same-sex households is rarer still. Among those who reported having a mother who had a same-sex relationship, 91 percent said they lived with their mothers when they were in the relationship. Fifty-seven percent reported living with their mother and her partner for more than four months, and 23 percent for at least three years. Among young adults whose fathers had a same-sex relationship, 42 percent said they lived with them during the relationship; 24 percent said they lived with their fathers and fathers’ partners for more than four months; and less than 2 percent for at least three years.

Only two respondents whose mothers had a same-sex relationship reported that this living arrangement lasted all 18 years of their childhood. No respondents with fathers who had a same-sex relationship reported such longevity.

The NFSS surveyed young adult respondents about their own relationship history and quality, economic and employment status, health outcomes, abuse history, educational attainment, relationship with parents, psychological and emotional well-being, substance use, and sexual behaviors and outcomes.

Compared to young adults in traditional, intact families, young adults whose mothers had a same-sex relationship tended to fare worse than their peers in intact biological families on 24 of the 40 outcomes examined. For example, they were far more likely to report being sexually victimized, to be on welfare, or to be currently unemployed.

Young adults whose fathers had a same-sex relationship showed significant differences from their peers in intact families on 19 of the outcomes. For example, they were significantly more likely to have contemplated suicide, to have a sexually transmitted infection, or to have been forced to have sex against their will.

These differences take into account the respondent’s age, race/ethnicity, gender, mother’s education, perceived family of origin’s income, whether or not the respondent was ever bullied, and the legal status of same-sex relationships in the respondent’s current state of residence. In other words, the study compared respondents who were identical on these characteristics, except for parental relationship status.

A significant improvement on the limited research to date on child outcomes and same-sex parenting, this new study marks an important development in the research. As findings based on studies using the NFSS and other large, nationally representative data on same-sex parents and their children accumulate, a more generalizable picture will begin to emerge.

At present, far too little is known about this new household form into which activist courts are pushing America—and much of what has been presented to date gives an inaccurate picture of the reality that children of same-sex parenting have experienced.

NFSS project director Dr. Mark Regnerus concludes in a piece running on Slate today that “the stable, two-parent biological married model [is] the far more common and accomplished workhorse of the American household, and still—according to the data, at least—the safest place for a kid.”