AUSTIN, TEXAS, June 13 (CNA/EWTN News) .- Children brought up by partners in same-sex relationships are encountering more difficulties in adulthood than their conventionally-raised counterparts, according to new findings published June 10.

"On 25 out of 40 different outcomes, there are statistically-significant differences between adult children who grew up with a mother who had a lesbian relationship and those who told us their biological mother and father were, and still are, married," researcher Mark Regnerus told CNA on June 12.

Children of these same-sex households were found to have lower average income levels as adults, along with more physical and mental health problems and more instability in their romantic relationships. They also showed higher levels of unemployment, smoking, need for public assistance and involvement in crime.

"Household instability," Regnerus said, was "a hallmark" of households whose parents engaged in same-sex relationships, whether those households were "led by a mother or father."

Regnerus' findings, published in the July issue of Social Science Research, drew on data from the New Family Structures Study. That survey measured differences in 40 social and personal indicators, among 3,000 Americans ages 18 to 39 who were raised in eight different types of households.

The new findings challenge data cited in 2005 by the American Psychological Association, which claimed 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."

According to Regnerus, some of these influential studies have relied too heavily on small or non-representative population samples - focusing mainly on highly educated, white same-sex couples, in order to draw conclusions about same-sex parenting in general.

"Most conclusions about same-sex parenting have been drawn from small, convenience samples, not larger, random ones," Regnerus said in a June 11 statement released by the University of Texas at Austin.

"The results of that approach have often led family scholars to conclude that there are no differences between children raised in same-sex households and those raised in other types of families. But those earlier studies have inadvertently masked real diversity among gay and lesbian parenting experiences in America."

The researcher told CNA he approached the project with "no idea what the data would reveal." Upon analysis, he said, "it's revealed far greater instability in the households of parents who've had same-sex relationships."

In his June 10 announcement of the paper, Regnerus said his "most significant" finding "is arguably that children appear most apt to succeed well as adults when they spend their entire childhood with their married mother and father, and especially when the parents remain married to the present day."

The sociologist said that his study has already "stirred up a hornet's nest" of "intense and frequent" criticism, which he called "disproportionate to the study's limitations."

The paper has been attacked by the Family Equality Council, Human Rights Campaign, Freedom to Marry, and the Gay and Lesbian Alliance against Defamation.

Regnerus described it as "unfortunate" that his own study "is high-quality and being maligned." He suggested his findings should simply be held to the standards of "normal science," which "exhibits disagreements among researchers about how to measure this or that."