Only a small fraction of symptom combinations in mental disorders are common, with most combinations being reported by less than 1% of participants, according to a recent study.
A cross-sectional study examines the structured patterns of symptom combinations in mental disorders, focusing on polythetic definitions. Researchers conducted this study using theoretical arguments, simulations, and empirical analyses of data from 155,474 participants to explore symptom heterogeneity.
The study, published in JAMA Psychiatry, included 41,543 participants with posttraumatic stress disorder (PTSD), 46,259 participants with major depressive disorder (MDD), 3,959 participants with schizophrenia, and 63,742 participants with anxiety disorders. The average age of participants was 47.5 years with a standard deviation of 14.8 years. The sample included 33,933 females (21.8%) and 121,541 males (78.2%).
The research used theoretical frameworks, simulations, and secondary analyses of four datasets from sources such as the National Institute of Mental Health Data Archive and the Department of Veteran Affairs. It's worth noting that 3 of the 4 samples comprised veterans, which could limit generalizability.
Researchers noted that between 41.7% and 99.8% of symptom combinations occurred in less than 1% of participants, whereas the top 1% of the most common combinations were seen in 33.1% to 78.6% of the participants. The most common combination alone had a prevalence of 33.1% to 46.2% across samples. This pattern was consistent across disorders including PTSD, MDD, schizophrenia, and anxiety disorders.
The study found that symptom combinations within each disorder follow a specific pattern. A few combinations are highly probable, while the majority have a very low probability of occurrence. This structured heterogeneity includes both common, prototypical symptom presentations and numerous atypical combinations.
Importantly, the researchers argue that this pattern is inherent to symptom-based systems of mental disorders and is a direct consequence of polythetic symptom-based definitions. Differences in individual symptom prevalence and interrelations result in the described differences in probabilities of symptom combinations.
The study discusses implications for research and diagnostic practices, including the need to consider this pattern when revising diagnostic criteria or conducting research based on symptom combinations. The researchers also developed an interactive simulation tool to further illustrate their findings.
Full disclosures can be found in the published study.
