PSA2016: The 25th Biennial Meeting of the Philosophy of Science Association

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Comorbidity and psychiatric disease classification

Comorbidity and psychiatric disease classification

High rates of comorbidity puzzle professionals and researchers in psychiatry. Epidemiological studies suggest that up to 45% of psychiatric patients satisfy the criteria for more than one disorder within one year (Kessler et al., 2005). To what extend do these rates depend on classification choices in the Diagnostic and Statistical Manual of Mental Disorders (DSM)? Some authors argue that comorbidity is an artificial by-product of specific classification choices such as including more diagnoses (e.g., Aragona 2009). Against this, other researchers in psychiatry contend that comorbidity is a real phenomenon tied up with the nature of psychiatric disease itself, and that it indicates commonalities in the causal background of different disorders (e.g. Andrews et al., 2009). In other words, the field is divided over the exact status that comorbidity should be allotted between, what may be called, a constructivist and a realist camp.

Our poster offers an alternative understanding of the ontological, or else epistemological status of comorbidity. We propose a position that escapes the opposition between constructivists and realists, showing that high comorbidity rates indeed derive from the classification system but at the same time reveal something genuine about psychiatric disorders. This position can be illuminated by referring back to a debate in the philosophy of science, to do with the ontological and epistemological status of geometrical descriptions of physical space. In this context a very similar position has surfaced under the name of conventionalism (Poincaré 1905, Reichenbach 1958). On the one hand, the geometrical model of physical space offers a robust picture of reality, but on the other hand it only does so relative to a set of coordinative definitions. We maintain that the ontological and epistemological status of comorbidity findings are very similar. They offer a robust picture of the world of psychiatric disorders, yet they do so relative to a number of conventions.

Our poster illustrates with empirical data about comorbidity between anxiety and depression symptoms in the general population (LifeLines, n=74,092) that a conventionalist position illuminates the interplay between classification choices and characteristics of patients in the psychiatric domain. Moreover, conventionalism fits well with the use of classifications in psychiatry and offers advantages for psychiatric research. With reference to recent attempts to redefine psychiatric diseases, we show that a conventionalist position leaves room for evaluating new definitions of psychiatric disorders. Ultimately this might lead to progress in research and better treatments for patients suffering from psychiatric comorbidity.

Andrews, G., et al. (2009). Exploring the feasibility of a meta-structure for DSM-V and ICD-11: Could it improve utility and validity? Psychol Med, 39(12), 1993-2000.
Aragona, M. (2009). The role of comorbidity in the crisis of the current psychiatric classification system. Philosophy, Psychiatry & Psychology, 16(1), 1-11.
Kessler, R.C., et al. (2005). Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the national comorbidity survey replication. Arch Gen Psychiatry, 62(6), 617-627.
Poincaré, H. (1980). Science and hypothesis. Dover Publications.
Reichenbach, H. (1958). The philosophy of space & time. New York, N.Y.: Dover.

Author Information:

Hanna van Loo    
University Medical Center Groningen

Jan-Willem Romeijn    
University of Groningen


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