A Categorical Approach to Depression by a Three-Dimensional System

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Abstract
Depressed moods do not arrive already hallmarked ‘endogenous’. Depressions do, however, arrive as perceivable phenomena and the domain of clinically important and conceptually connected items includes about 20 items. This domain can be subdivided into items relevant for the severity of the depression and items relevant for the diagnosis of depression. It has been argued that Rasch models rather than multivariate analysis are the adequate models when studying the internal consistency of rating scales. Applying the Rasch models, it was found that 10 items have an additive relationship for the severity of depression and that 5 items were additively related for endogenous depression, whereas five other items were additively related for reactive depression. Moreover, it was found that the dimension of severity should be transformed to three categories: no depression, minor depression and major depression. The two dimensions: endogenous and reactive depression, respectively, should be transformed to the categories: definite endogenous depression, combined endogenous and reactive depression, definite reactive depression, probable endogenous depression and probable reactive depression. These categories for severity and for the diagnosis of depression have a high internal consistency. However, we still need studies to verify the external validity of these concepts.