updated 4:58 p.m. ET, Mon., Jan. 4, 2010

About half of Americans with major depression do not receive treatment for the condition, and in many cases the therapies are not consistent with the standard of care, according to a new study.

The study also showed that ethnicity and race were important factors in determining who received treatment, with Mexican Americans and African Americans the least likely to have depression care.

While many people can feel sad from time to time, a depressive disorder occurs when these feelings start to interfere with everyday life, preventing someone from functioning normally, according to the National Institutes of Health (NIH). The condition can be debilitating, hindering a person's ability to work, sleep and eat. A combination of factors likely contributes to the disorder, including imbalances in brain chemicals, genetics, and stressful situations, the NIH says.