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The lingering effects of the Great Recession have contributed to a boom in the number of unmarried couples who live together, but a new survey from the Pew Research Center has found that those couples tend to be less happy than their married counterparts.

The survey results show high public support for unmarried couples who live together, with majorities of every age group saying they find it acceptable to live with an unmarried partner. At the same time, the share of American adults who live with an unmarried partner has more than doubled since 1993, to 7% from 3%. The share of American adults who are married is 53%.

Juliana Horowitz, a co-author of the report, said of the unmarried couples, "A large share said either themselves not being ready financially or their partner not being ready financially was a major reason they were not married to their partner."

Horowitz said "love and companionship topped the list" of reasons unmarried couples cited when asked to explain their decision to move in together. But roughly 40% said convenience or finances were a major factor. In contrast, just 13% of married couples said financial considerations played a part in their decision to wed.

It used to be considered somewhat taboo for a couple to live together if they were not married — hence the term "living in sin" — but those attitudes have changed, researchers said.

A slim majority of Americans, 53%, said society would be better off if long-term couples got married. But 69% of Americans said it was acceptable to live with a romantic partner even if you have no plans to get married, while 16% said it was OK only if a couple sees a wedding in their future. A majority also said unmarried couples could raise children just as well as married couples could.

But all this acceptance does not mean there are no troubles for unmarried couples.

According to the survey, unmarried couples report significantly less satisfaction in their relationships than do married couples, who report higher levels of trust in their partners' honesty, fidelity and spending habits. It said that 58% of married adults said their relationship was "going very well," compared with 41% of unmarried people who live with a partner.

That pattern held true across a broad range of areas, from chores to parenting.

But when it comes to sex, similar shares of married and unmarried cohabitants say they are "very satisfied" with their sex lives, 36% to 34%.

Horowitz said it was not clear from the results why married people said they were so much happier than unmarried couples.