(CNN) - One day before the Supreme Court hears a high profile case on same-sex marriage, a new national poll indicates that the percentage of Americans who say they have a family member or close friend who is gay or lesbian is on the rise.
That increase matches a jump in the percent of the public who support legal same-sex marriages.
According to a CNN/ORC International survey, 57 percent say they have a family member or close friend who is gay or lesbian, up 12 points from 2007.
"The number of Americans who support same-sex marriage has risen by almost the same amount in that time - from 40 percent in 2007 to 53 percent today - strongly suggesting that the rise in support for gay marriage is due in part to the rising number of Americans who have become aware that someone close to them is gay," said CNN Polling Director Keating Holland.
"Some people have recently taken to calling it the 'Rob Portman effect,' after the Republican senator from Ohio who learned that his son is gay and changed his position on gay marriage as a result," adds Holland. Portman made his announcement recently in an exclusive television interview with CNN.
The survey's Monday release comes a day before the Supreme Court hears a challenge to California's Proposition 8. On Wednesday, the justices will hear a challenge to the federal government's Defense of Marriage Act.
Both measures define marriage as a union between a man and a woman. According to the poll, people who say they know someone who is gay or lesbian are more likely to be younger and more likely to have attended college, with women more likely to say that than men.
Not surprisingly, support for gay marriage is highest among women, college educated Americans, and the young.
"Attitudes toward homosexuality are the result of many complex, interrelated factors. Past polling, for example, has also shown that support for gay marriage has risen during a time when a growing number of Americans believe that homosexuality is something a person is born with. But years of polling suggests that the growing number of Americans who know someone who is gay has contributed to an environment in which gay marriage now receives support from a majority of Americans," Holland said.
The new poll was conducted March 15 to 17 for CNN by ORC International, with 1,021 adult Americans questioned by telephone. The survey's overall sampling error is plus or minus three percentage points.