The study was controlled to eliminate the influence of factors that could impact the timing of sexual intimacy, such as religion, education, relationship length and the number of previous sexual partners.
The study authors cited "relationship inertia," a theory from earlier research, as a reason poorly matched couples stay together. As time goes on, partners feel "constrained" by the complexities of the situation when they may have more wisely parted company, the research noted.
"You get on this escalator and begin sliding into a relationship, rather than deciding in a thoughtful way to become more involved," said Busby. "People say, 'I've invested four or five years in this relationship' or 'We bought a house together,'" he added, noting that "the relationship becomes too complicated to leave."
Busby cautioned against concluding that premarital sex necessarily leads to a bad marriage, however.
"Just because someone has sex early in a relationship doesn't mean the marriage is doomed," he said. "We're not saying that."
Busby also said the study group was more white and educated than a random sample of Americans would be, so more research is needed to draw stronger conclusions.
But the study, published in the December issue of the Journal of Family Psychology, suggests that an early focus on sex may lead to "more brittle marriages."
"You can have great sex with someone you have an incompatible personality with," Busby pointed out. "Sex is important, but it is not the only important thing in marriage."
The study drew praise from another expert on interpersonal relationships.
"The impulse to assess sexual chemistry early in a romantic relationship, if not before, is a popular one," said Mark Regnerus, author of the book Premarital Sex in America'/>"/>
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