Severe flaws and limitations exist in the scientific research into the relatively new phenomenon of same-sex parenting, argue preeminent political scientists Leon R. Kass and Harvey C. Mansfield in a brief filed with the Supreme Court by Nelson Lund.

The scholars urge the Court not to redefine marriage based on the new and inconclusive research. The academic studies on same-sex parenting purporting to show “no differences” are, Kass and Mansfield argue, “subject to severe constraints arising from limited data” and a lack of “replicable experiments.” They argue:

Even if same-sex marriage and child rearing by same-sex couples were far more common than they now are, large amounts of data collected over decades would be required before any responsible researcher could make meaningful scientific estimates of the effects.

Current research in favor of same-sex parenting is based on limited data. One study sample relied on data gathered at “entirely lesbian events, in women’s bookstores, and in lesbian newspapers.” Most relied on reports by parents regarding their children’s well-being “while the children were still under their own care.”

Most social scientists have ignored the findings of Mark Regnerus (see Heritage discussions of his study here and here), whose study used a large and randomized sample of grown children rather than reports from a narrow selection of parents. This study found that children whose parents had same-sex relationships suffered more from excessive drinking, drug use, and lower educational performance and socialization than children of opposite-sex parents. It, too, has limitations, and more research is needed.

As Kass and Mansfield write:

There could conceivably come a time when supporters of traditional marriage are compelled by scientific evidence to acknowledge that same-sex marriage is not harmful to children or to society at large. That day is not here, and there is not the slightest reason to think it is imminent. It is no less possible that scientific evidence will eventually show that redefining marriage…does have harmful effects on our society and its children. That day is also not yet here, but there is no basis for this or any other court to conclude that it will never arrive.

Time and the lack of large samples prohibit academic research from making reliable conclusions on same-sex parenting. Claims of no difference between family structures are based on inadequate evidence, and, at least in some cases, ideology.

Kass and Mansfield highlight late Senator Daniel Moynihan’s (D–NY) statement that “social science is rarely dispassionate, and social scientists are frequently caught up in the politics” surrounding their work. The current political climate has influenced much of the existing research on issues regarding same-sex parenting. As Norval Glenn wrote:

Given the widespread support for same-sex marriage among social and behavioral scientists, it is becoming politically incorrect in academic circles even to suggest that arguments being used in support of same-sex marriage might be wrong.

Social science motivated by politics and ideology should not be used by the Court to decide the legal question of the constitutionality of marriage. As Kass and Mansfield argue:

[C]laims that science provides support for constitutionalizing a right to same-sex marriage must necessarily rest on ideology. Ideology may be pervasive in the social sciences, especially when controversial policy issues are at stake, but ideology is not science.

They’re right. Ideology is not science, nor should it be made law. The Supreme Court should respect the Constitutional authority of citizens and their elected officials to make marriage policy.

Kayla Griesemer is currently a member of the Young Leaders Program at The Heritage Foundation. For more information on interning at Heritage, please click here.