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Friday, February 25, 2011

DIAGNOSIS AND CLASSIFICATION IN PSYCHOPATHOLOGY

DIAGNOSIS AND CLASSIFICATION IN PSYCHOPATHOLOGY

The psychiatric diagnosis is essential to all clinical, research, and policy endeavors involving mental health. For clinicians, diagnostic systems identify at-risk individuals for prevention services; select other cases for referral and brief treatment; in more serious cases they may suggest special courses of treatment that have been empirically tested; and they confer on third-party payers the responsibility of honor charges for that treatment. most diagnostic systems are categorical or, like DSM-III, III-R, and IV, “classquantitative”. Such systems permit additional nuance, such as severity ratings, codes for the presence/absence of special features, and so on, but they require, above all, diagnostic classification. “Man is by nature a classifying animal. . . Indeed, the very development of the human mind seems to have been closely related to the perception of discontinuities in nature” .Raven and his colleagues used the term folk taxonomy to indicate the predisposition of subgroups, especially guildlikegroups of craftsmen, to establish categorical nomenclatures (folk taxonomies) for classifying objects in nature that are of special interest to them. Thus, potters have extensive taxonomies of clay, stonecutters of hardness and grain, and so forth. In a classic monograph, the cognitive psychologist .there are nonarbitrary or “natural” categories that form around perceptually salient natural prototypes. Such natural categories could, of course, serve as the basis for the folk taxonomies described by Raven and his coauthors. Rosch explained the key attributes of natural categories: (1) they are nonarbitrary; (2) they are partitioned from continua; (3) they cannot, by use of normal language, be further reduced to simpler attributes; (4) they are easily learned by novices; (5) they serve as natural structures for the organization of more knowledge; and 6) they have indistinct boundaries, encompassing both clear-cut and marginal examples.
human beings tend to categorize and classify things in roughly the same way, across cultures and, presumably, across historical eras. It seems a characteristically human thing to do. In a more recent monograph, Lilienfeld and Marino (1995) extended a Roschian analysis to psychiatric diagnosis, arguing that major psychopathologic entities such as schizophrenia or bipolar illness are, like Roschian or natural prototypes, partitioned from the continuum of human behavior, irreducible to simpler concepts, understood analogously across cultures, have good and bad examples, and so on. This view complements the conceptualization of psychiatric diagnosis as a problem in prototype categorization. Cantor and her colleagues proposed that psychiatric diagnosis follows not a classic categorization model (universally accepted criteria, high agreement about class membership, and within-class homogeneity of members) but rather a prototype categorization model. Prototype categorization assumes (1) correlated—not necessarily pathognomonic—criteria for class membership, (2) high agreement among classifiers only when classifying cases that demonstrate most of the correlated criteria for class membership (disagreement is expected when cases have a marginal number of category features, or when they bear features from more than one category), and (3) heterogeneity of class membership, because criteria are only correlated, not pathognomonic. Thus, whereas systems of psychiatric diagnosis have their critics—and many of their arguments will be reviewed later— there is nothing arcane, much less unprecedented, in the actions
of a mental health professsional who, encountering a new case, lifts a copy of the DSM from her desk, matches the properties of the new case to one or more of the DSM categories, and then uses the diagnostic result to select treatment, to make a referral, or to rule the case in or out of a research protocol. To the contrary, what the mental health professional is doing is as old, as honored, as universal, and as essentially human as the crafts themselves (Nathan & Langenbucher, 1999).

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