"We used cluster analyses to better describe the characteristics of depressive symptoms -- affective, cognitive and somatic," Dr. Sergio Baldassin of the ABC Regional Medical School in Santo Andre, Brazil, said in a statement.

"This is the first study to directly evaluate, in a cross-sectional design, the characteristics of depressive symptoms by applying such clusters."

The core symptoms of a depressive mood were based on the students' reported levels of sadness, dissatisfaction, episodes of crying, irritability and social withdrawal. The cognitive cluster assessed pessimism, sense of failure or guilt, expectation of punishment, dislike of self, suicidal ideation, indecisiveness and change in body image.

The somatic cluster assessed the presence of slowness, insomnia, fatigue, loss of weight and loss of sexual interest.

The study, published in the journal BMC Medical Education, found a high prevalence toward depressive symptoms among medical students -- 38 percent had at least 10 of a possible 63 symptoms of depression.

The cluster analysis also found depression scores were at its worst in the internship years probably due to feelings of fear and insecurity about entry into the hospital environment in addition to sleepless nights on call, devoid of friend and family support, Baldassin said.