A new study of Chinese-Caucasian, Filipino-Caucasian, Japanese-Caucasian and Vietnamese-Caucasian individuals concludes that biracial Asian Americans are twice as likely as monoracial Asian Americans to be diagnosed with a psychological disorder.

The study by researchers at the Asian American Center on Disparities Research at the University of California, Davis, was reported Sunday at the annual meeting of the American Psychological Association in Boston.

"Up to 2.4 percent of the U.S. population self-identifies as mixed race, and most of these individuals describe themselves as biracial," said Nolan Zane, a professor of psychology and Asian American studies at UC Davis. "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."

Zane and his co-investigator, UC Davis psychology graduate student Lauren Berger, found that 34 percent of biracial individuals in a national survey had been diagnosed with a psychological disorder, such as anxiety, depression or substance abuse, versus 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 study included information from 125 biracial Asian Americans from across the U.S., including 55 Filipino-Caucasians, 33 Chinese-Caucasians, 23 Japanese-Caucasians and 14 Vietnamese-Caucasians.

The information was obtained from the 2002-2003 National Latino and Asian American Study, the largest nationally representative survey ever conducted of Asian Americans. Funded by the National Institute of Mental Health, the landmark survey involved in-person interviews with more than 2,000 Asian Americans nationwide. The survey yielded a wealth of raw data for researchers to analyze for insights into Asian American mental health.

Zane and Berger did not look at the mental health of non-Asian Americans.

Future research should investigate the factors that explain the higher rate of diagnosed psychological disorders among biracial Asian Americans, Zane said. Possibilities include influences of ethnic identification and experiences of ethnic discrimination.