Understanding the severity of depression: Which symptoms of depression are the best indicators of depression...

In DSM-5, all symptoms of depression are considered equal representations of severity. In ICD-10, the type of symptom is considered in classifying severity. It is important to better understand if the defining symptoms of depression are differentially associated with overall severity so that severity categorization in diagnostic systems is most valid. In the present study from the Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project we examined the association between the individual diagnostic criteria for major depressive disorder (MDD) and global ratings of depression severity. We thus examined whether there is support for the ICD-10 approach in which some symptoms are better indicators of severity than are other symptoms.

Patients were evaluated with a semi-structured interview and the presence of each symptom of MDD was recorded. Patients were also rated on the Clinical Global Index of severity (CGI-S).

All 9 DSM-5 criteria were significantly correlated with the CGI with suicidality having the highest correlation. A regression analysis found that all 9 criteria were significant predictors of the CGI. At the symptom level, 15 of the 17 symptoms were significantly correlated with the CGI (all except increased appetite and increased weight).

There were differences between the symptoms of depression in their association with severity with suicidal ideation, depressed mood, and anhedonia having the highest correlations with severity whereas some symptoms were not significantly associated with severity distinctions. Future descriptions of the severity of depression should not consider all criteria as equal representations of severity.