Census data released yesterday shows that conservative states such as Utah and Wyoming have some of the highest proportions of gay couples who call themselves married.

According to the annual American Community Survey, almost 150,000 gay couples (more than one in four), call each other husband or wife, despite estimates that no more than 32,000 are actually married or in a civil union.

Unsurprisingly, the researchers found that gay couples are strikingly similar to straight couples in terms of average age, income and numbers who have children.

Thirty-one per cent of gay couples who called themselves married had children, compared to 43 per cent of heterosexual married couples. Although gay couples who did not call themselves married were less likely to have children, they were more likely to be younger than those who said they were married.

Gary Gates, the University of California Los Angeles demographer who carried out the analysis, told Associated Press: “It’s intrinsically interesting that same-sex couples who use the term spouses look like opposite-sex married couples even with a characteristic like children.

“Most proponents of traditional marriage will say that when you allow these couples to marry, you are going to change the fundamental nature of marriage by decoupling it from procreation. Clearly, in the minds of same-sex couples who are marrying or think of themselves as married, you are not decoupling child-rearing from marriage.”

Massachusetts and Vermont had the highest proportional numbers of gay couples who were married or considered themselves married, which was deemed logical as these two states have had civil unions for years. Massachusetts legalised gay marriage in 2004, while Vermont followed suit this year.

However, Hawaii, Utah and Wyoming came next. None of these states allow civil unions or gay marriage and the latter two are known to be particularly conservative.

Researchers said this was “evidence that there are clearly couples in conservative parts of the country who do use these terms and do see their relationships in that framework”.