More Americans are marrying outside of their racial groups, a look at census data showed.

University of Michigan researchers compared the number of interracial marriages listed in the 1990 census with those in previous decades.

They found that 8 percent of black men between the ages of 25 and 34 in 1990 were married to someone of another race, compared with fewer than 2 percent in the 1940s and ‘50s.

Among white men in the same category, about 4 percent were married to someone of another race, compared with about 1 percent in the ‘40s and ‘50s.

The percentage of black women ages 25 to 34 married in 1990 to someone of another race was 4 percent, compared with about 1 percent in the ‘40s and ‘50s.

Among white women in the same age category, 3 percent were married to someone of another race, compared with fewer than 1 percent in those two decades.

The study analyzed Census data on marriages between whites, blacks, Native Americans and native-born Asians and Hispanics.

The military has a high rate of interracial marriage, the researchers said, and that may be a key reason for the change, said Reynolds Farley, the lead researcher.

White men who served in the military were three times as likely to marry black women as white men who never served, the study said. White women who served were seven times more likely to marry outside their racial group as those who never served.

Some people who have married outside their races say the results simply show greater tolerance of mixed couples since the years when many states outlawed interracial marriages.

“Hopefully people are just more enlightened - their social circles are broadened,” said Kimberly Crafton, 40, a black woman whose husband is white.