One of the most controversial and complex issues affecting the field of clinical psychology and psychiatry is how to integrate two distinct conceptualization of psychiatric conditions. Our field has been dominated by a disease model, in which psychiatric disorders are viewed as discrete categories. That is, a disorder is either present or absent (e.g., you have schizophrenia or you don’t). On the other hand, research also suggests that most disorders exist on a dimension, and may be extensions – albeit extremes- of natural experiences. Depression is one of the most commonly used examples. We all feel sad sometimes. But when does our sadness stop being sadness and become clinical depression? Where is the line? Is the line arbitrary?
The debate regarding this issue is far from settled, and the evidence for and against both positions is strong and ever evolving. This usually means that both theories are right- and wrong, and that the real answer lies somewhere in between.
While reading the last issue of the Journal of Child Psychology and Psychiatry I came across a study that is likely to move this debate forward, at least in regards to child depression. The article provided data from 3 separate studies with 3 separate samples. The first study included 1,372 non-clinical school children between the ages of 5 and 19 . The second study included 159 children with diagnoses of clinical depression ages 9 to 13. The third study included 124 community school children ages 11-16.
In the first study the children completed the Child Depression Inventory (CDI), which is the most commonly used depression scale for children and adolescents. The authors used an advanced statistical method called a taxometric analysis (MAXCOV, MAMBAC, MAXEIG, LMODE, and MAXSLOPE) to examine whether patterns of responses in the CDI could identify a ‘taxon’ or a specific pattern that is inconsistent with a dimensional view of depression symptoms and instead suggestive of a discrete category.
- In the first study the authors found that their taxometric analyses supported the presence of a taxon of child depression, which supports a categorical view of the disorder.
- In the second study the authors conducted the same taxometric analysis but using a clinical population of children who had been diagnosed with child depression. The results were consistent with the first study. The taxometric analysis suggested the presence of a taxon.
- Finally, in the third study the authors tested the validity of the taxon by examining it against the tripartite model of depression. Specifically the authors wanted to explore whether this taxon was not related to anxiety-specific factors and instead only related to depression-specific factors. The results also supported the presence of a taxon, and the taxon-based items from the CDI were even better than the total CDI in predicting constructs associated with depression (e.g., low positive emotionality).
All in all, this study suggests that clinical depression is a categorical construct rather than a dimensional one. This is actually surprising because most recent studies in child depression have suggested that this condition is a dimensional construct. Why the major discrepancy? The authors discussed a number of methodological limitations of previous studies that probably prevented them from identifying a taxon. Specifically, the authors provided a strong argument indicating that the sample size used in previous studies made the studies ‘underpowered’ in their ability to identify a taxon. That is, even if a taxon existed, the sample size used in past studies would have made the identification of such a taxon impossible.
Where does this leave us? There is no doubt that each specific symptom of depression is dimensional in nature. People feel different levels of sadness, anhedonia, sleep problems, even suicidality. But it seems that there is a point when these symptoms converge, at a specific intensity, to create a situation – a taxon- that is qualitatively different than normative functioning. I think research will move towards the integration of taxometric and dimensional approaches to psychopathology. The available data supports both views, and we will likely abandon the notion that both approaches are incompatible.
The Reference: Richey, J., Schmidt, N., Lonigan, C., Phillips, B., Catanzaro, S., Laurent, J., Gerhardstein, R., & Kotov, R. (2009). The latent structure of child depression: a taxometric analysis Journal of Child Psychology and Psychiatry DOI: 10.1111/j.1469-7610.2009.02085.x
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