The analysis also concludes that both genders diagnosed with PTSD equally suffer from depression. Since women tend to report more symptoms of depression than men, this contradicts a general belief that women are more inclined to struggle with both.

The findings were based on an analysis of 57 peer-reviewed studies, representing data on 6,670 people (civilians and military personnel) who suffered from PTSD. Researchers conclude that 52 percent of the PTSD cases also reported symptoms of depression.

Before the study, estimates for individuals having both major depression disorder (MDD) and PTSD had ranged anywhere from 20 to 80 percent.

The research represents the first comprehensive analysis of peer-reviewed literature on people with PTSD and MDD.

PTSD is an anxiety disorder resulting from a traumatic incident in which flashbacks or unshakable thoughts about the trauma are common. MDD is characterized by an overwhelming and lingering sense of sadness and hopelessness. Symptoms can range from "feeling the blues" to thoughts of suicide.

"If individuals do not get a comprehensive assessment of what's bothering them, one or the other can be missed," said Case Western Reserve research associate Nina Rytwinski, the study's lead investigator and a researcher with the National Institute of Mental Health-funded PTSD project directed by Norah Feeny, PhD, from Case Western Reserve University and Lori Zoellner, PhD, from the University of Washington. "This high co-occurrence rate accentuates the importance of routinely assessing for both disorders."

The findings also suggest important implications for improving how men with PTSD are treated. Health-care providers tend to identify depression more frequently in women, while men can exhibit symptoms of depression that are misattributed to PTSD, Rytwinski said.

"The biases against men with PTSD symptoms put them at risk for under diagnosis and under treatment of a major depressive disorder," she said.

Researchers narrowed about 1,500 studies on PTSD and MDD to the 57 published peer-reviewed studies. They focused on research about individuals who had experienced some physical or sexual assault trauma.

By recognizing how frequently people experience both disorders, clinicians may better address barriers to completing therapy, personalized treatment and overall care, the researchers report.

Study contributors included: Norah Feeny, PhD, Department of Psychological Sciences, and Michael D. Scur, BA, Department of Psychiatry at the Case Western Reserve University School of Medicine, and Eric A. Youngstrom, PhD, Department of Psychology at University of North Carolina at Chapel Hill.