MADD was developed in recognition that a substantial number of persons have clinically significant mood and anxiety disorder symptomatology yet fall below the thresholds for any existing mood or anxiety diagnosis. persons diagnosed with MADD cannot be comfortably or distinctly diagnosed with either an anxiety or a mood disorder.

University of Illinois at Urbana-Champaign

New diagnoses added to the nomenclature reflect not so much the discovery of a previously unrecognized disease, pathogen, or lesion but are instead to efforts to fill gaps among existing categories. However, these new diagnostic categories can create additional boundary confusions. 

Generalized social phobia

Schizoaffective disorder

Mixed anxiety-depressive disorder

These three diagnoses are examples because they are on the borders of domains of psychopathology that have been regarded as relatively distinct.

Boundary disputes

Widiger, T. A., & Samuel, D. B. (2005). Diagnostic categories or dimensions? A question for the Diagnostic and statistical manual of mental disorders--. Journal of abnormal psychology, 114(4), 494. https://doi.org/10.1037/0021-843X.114.4.494

Diagnostic categories or dimension? A question for the Diagnostic and Statistical Manual of Mental Disorders -- Fifth Edition

It is consistent with the definition of a phobia: a "persistent, irrational fear of a specific object, activity, or situation". There are four most common situations avoided by a person with social phobia: speaking or performing in public, using public lavoratories, eating in public, and writing in the presence of others.

Generalized social phobia

At first, it lacked the specific and explicit criterion set. A consensus could not be  reached on its defining features in large part because it represented the grey area between schizophrenia and mood disorder. Schizoaffective disorder might be best understood as an inherently ambiguous condition that occupies the overlapping boundary between schizophrenia and mood disorder. 

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