The University of California, Davis, researchers based their study on information from the 2002 to 2003 National Latino and Asian-American Study. The sample included 125 biracial Asian-Americans in the United States including: 55 Filipino-Caucasians, 33 Chinese-Caucasians, 23 Japanese-Caucasians and 14 Vietnamese-Caucasians.

"Up to 2.4 percent of the U.S. population self-identifies as mixed race, and most of these individuals describe themselves as biracial," Nolan Zane of the University of California, Davis, said in a statement. "We cannot underestimate the importance of understanding the social, psychological and experiential differences that may increase the likelihood of psychological disorders among this fast-growing segment of the population."

Among the biracial individuals in their national survey the researchers found 34 percent had been diagnosed with a psychological disorder -- such as anxiety, depression or substance abuse -- compared to 17 percent of monoracial individuals. The higher rate held up even after the researchers controlled for differences between the groups in age, gender and life stress among other factors.

The findings were reported at the annual meeting of the American Psychological Association in Boston.