"Our findings support the hypothesis that the assumption of homogeneity of the prevalence of depression across Hispanic groups is not tenable," said study researcher Dr. Yang of Hebrew SeniorLife's Institute for Aging Research in Roslindale, Mass. "Furthermore, Puerto Ricans experienced a significantly higher number of depressive symptoms and prevalence of depression than did the three Hispanic groups in the study."

Yang and colleagues say further research is needed to determine Puerto Ricans' exposure to factors that account for higher prevalence of depression than other Hispanic groups and whites living in the United States.

The study, published in the Journal of Gerontology: Psychological Sciences, found nearly 7 percent of Puerto Ricans -- who make up 11 percent of the Hispanics 65 and older -- suffer from major depression, compared to Mexican-Americans, Cuban-Americans and Hispanics from Central and South America. Only 2.8 percent of Mexican-Americans and 2.5 percent of Cuban-Americans suffer from major depression.

The researchers examined 759 Hispanics over the age of 59. Data was obtained from the University of Michigan's Health and Retirement Study.