Our new study titled “Depression is not a consistent syndrome: An investigation of unique symptom patterns in the STAR*D study” was published in the Journal of Affective Disorders (PDF).
In the paper we examine the degree of heterogeneity of Major Depression (MD). The DSM-5 defines a host of depression symptoms, which are commonly added up to sum-scores that reflect overall depression severity. This implies that depression symptoms are interchangeable indicators of the same underlying condition. It further implies that all patients with MD have the same disorder, justifying the search for things like “depression risk factors” and “depression biomarkers”.
Therefore, we wanted to investigate how much depressed individuals actually differ in their symptoms. Using a conservative strategy to estimate profiles, we identified 1030 unique depression symptom profiles in 3703 depressed patients. 83.9% of these profiles were endorsed by five or fewer subjects, and 48.6% were endorsed by only one single individual.
The results could have shown that most patients fit into a few common patterns, but the most common symptom profile had a frequency of only 1.8%. This substantial symptom variation among individuals with the same diagnosis calls into question the status of MD as a specific consistent syndrome. It stresses the importance of investigating specific symptoms and their dynamic interactions. Sum-scores obfuscate important insights, and the analysis of individual symptoms and their causal associations that is an important part of the ‘Psychosystems Project’ described on this website offers a way forward.