Katz’s nosological concept of depressive disorder is not clear to me.

Katz states:

“The constructs of the depressive disorder………….encompass affect or emotional components such as depressed mood, anxiety and anger, disturbed psychomotor performance, thinking, somatic functioning and social behavior elements” (Katz p.26).

The goal was to "devise methods for measuring the psychological facets as separate elements" Eleven constructs were described, then boiled down by principal component analysis to three dimensions, referred to as (1) Anxiety-agitation-somatization-sleep disorder, (2) Depressed mood-motor retardation and (3) Hostility-interpersonal sensitivity (Katz p. 35).

Katz argues that major depressive disorder should be viewed as multifaceted, rather than as a “whole "disorder”.  The disorder comprises opposing central nervous system states…(Katz p. 37).

Katz should clarify if he considers the term "depression" to refer to some single distinct class with multiple independent manifestations, like measles? Or perhaps to several symptomatically overlapping   classes, like typhoid and typhus?

The Galenists saw the manifestations of illness as the particular, but entirely variable, combination of the four humors. Is that like the independent interactions of the opposing neurotransmitters?  In contrast, Sydenham viewed disease as distinct in terms of phenomenology and course.

In particular, can Katz's primary statistical approach, factor analysis, resolve or deny the mixture problem: whether there are overlapping but distinct syndromes as opposed to a single syndrome with varying manifestations? Or, more drastically, whether both the mixture and syndrome concepts are ill advised? Is the proposed alternative that the conflictual interplay of independent components, neurotransmitters rather than humors, that generates symptomatic variety?

Donald F. Klein

March 13, 2014