Prolegomenon to the Clinical Prerequisite; Psychopharmacology and the Classification of Mental Disorders
(Volume 1)

Conceptual Development of Current Psychiatric Nosology

Thomas A. Ban and Antonio Torrez Ruiz

Methodology of Psychiatric Classification

Classification in general refers to the ordering of objects "into groups on the basis of their relationships" (Sokal, 1974). In the medical disciplines, similar to other disciplines, the "classificatory system" provides for "denomination," "qualification" and "prediction,” i.e., "common names, "descriptive features" and "probabilistic statements" about expected "course" and "outcome" of the diagnostic groups (Feinstein, 1922). Since the validity and usefulness of classifications are largely dependent on the strength of their prognostic implications, Kendell (1975) maintains that in a meaningful classification the boundaries between diagnostic groups "should be placed in such a way that the (diagnostic) categories are as homogenous as possible with respect to prognosis, including therapeutic responsiveness."

Classification of Psychiatric Classifications

In his paper on Methodological Issues in Psychiatric Classification, Jablensky (1988) proposed a "three-way classification of classifications which can be applied to the examination of psychiatric classifications." According to their "taxonomic strategy," classifications in psychiatry may be "phyletic," i.e., based on a "primary essence," or "phenetic," i.e., based on a "meticulous description of the appearance of objects"; according to the "cognitive operation involved," classifications may be "empirical" i.e., based on "observable facts," or "inferential," i.e., based on inferences or "guesses" about "possible underlying causes and processes"; and according to their "end product," classifications may be "monothetic," i.e., based on "classes" which "differ by at least one property which is uniform among the members of each (one) class," or "polythetic," i.e., based on "classes" which "share a large proportion of their properties but do not necessarily agree in the presence of any one property" (Beckner, 1959; Guze, 1978; Sokal, 1974).

Currently used diagnostic classifications in psychiatry are "polythetic taxonomies" (Guze, 1978) which are to a great extent based on a "phenetic" "taxonomic strategy." However, in spite of its "atheoretical approach," not even the DSM-III-R is a truly "empirical" classification, because its diagnostic concepts are derived from a "meaning (consensus) analysis," and not from an "empirical analysis" exclusively (Schwartz and Wiggins, 1986).

Numerical Taxonomy

Phenetic classifications today may employ "numerical taxonomy," a statistical approach which has become practically feasible only with the advent of computers and multivariate statistical techniques. In a manner "reminiscent of the position of logical positivism," "numerical taxonomy" would like to be free of assumptions and therefore treats, at the start of analysis, "all characters and attributes of being of equal weight" (Jablensky, 1988). Such an approach of course is eminently suited in testing the validity of clinical hypotheses and impressions.

One of the heuristically important findings in a clinical diagnostic study, which employed “numerical taxonomy,” was that inclusion of "social adjustment" variables with "psychopathological symptoms" and "personality characteristics," lowered the "predictive validity" of diagnoses at the time of the "index psychoses." In the same study, the "clusters" based on "psychopathological symptoms" and "personality characteristics" had good correspondence with diagnoses at the time of the "index psychosis" whereas the variables of "social adjustment" had not (Petho, 1984).

Concluding Remarks

In the foregoing, the essential prerequisites of a valid "psychiatric nosology" were described and the basic principles in the construction of such a "nosology" reviewed. It was emphasized that "psychiatric nosology" is based on the assumption (of philosophical materialism) that "naturally occurring mental illness" is an "objective reality"; and it was suggested that "mental disorders" must be studied in their "dynamic totality," i.e., in their (dialectic) "movements" and "changes" as they unfold within their specific "determining structure."

The role of "psychopathology" in general, and the importance of "phenomenology" in particular, in the diagnostic process was discussed. It was pointed out that "abnormal psychology" is not an adequate substitute for any of the "component disciplines" of "psychopathology"; and that none of the "component disciplines" of "general psychopathology" alone is an adequate substitute for "psychopathology," i.e., the integrating discipline, in the diagnostic process.

Attention was focused on the distinctiveness between "form" and "content" in terms of "psychopathological symptoms" and in terms of the "psychopathological process," i.e., "onset," "course" and "outcome"; and an attempt was made to demonstrate that it is the information on the "how," i.e., on the "form" and not the information on the "why," i.e., on the "content," which is of diagnostic significance.

Some of the "theoretical controversies," such as the controversy of "categorical" vs "dimensional" diagnoses, and the "hierarchy" of diagnoses, were reviewed; and some of the "methodological issues," such as "phyletic vs "phenetic" nosologies, "inferential" vs "empirical" classifications, and "monothetic" vs "polythetic" taxonomies, were examined.

Finally, the difficulties in constructing a "truly empirical" classification of psychiatric disorders were discussed, with special consideration to the possibility that confounding the exploration of "phenomenology" with the study of "meaningful connections" may impede the diagnostic process. The same applies to the broadening of the scope of information from "psychopathology" to "social adjustment" which instead of adding a new dimension may decrease the validity of diagnoses.