Psychiatric Diagnosis and Classification - ResearchGate

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14 PSYCHIATRIC DIAGNOSIS AND CLASSIFICATION and accessory symptoms of schizophrenia [37] and Schneider's distinction between ``first-rank'' and ``second-rank'' symptoms in the differential diagnosis of schizophrenia and affective psychoses [38] can be regarded as early precursors of modern diagnostic criteria. The wide acceptance of the current DSM and ICD criteria is largely due to their derivation from an extensive knowledge base including recent clinical, biological and epidemiological research data. In addition, DSM-III and its successors DSM-III-R and DSM- IV, as well as ICD-10, have undergone extensive field trials and their final versions have been shown to be highly reliable. It can be assumed that the diagnostic criteria of future classifications will be similarly field-tested to remove or reword ambiguous elements in them, but it is unlikely that improving further the reliability of classification will remain a major goalÐ in contrast to issues of validity which are beginning to dominate the agenda. It is now recognized that the reliability of a diagnostic classification tells us little about the validity of its rubrics. In fact, a highly reliable diagnostic system can be of dubious validity, and in such a situation high reliability is of little value. On the other hand, a diagnostic concept of demonstrable validityÐe.g. one with important external correlates like neurocognitive features, familial aggregation of cases, or prediction of treatment response, may command poor diagnostic agreement. This is particularly likely to occur if the diagnostic category is of low sensitivity but high specificity, as shown by Rice et al. [39] for the diagnosis of bipolar II affective disorder. By and large, however, reliability imposes a ceiling on the evaluation of validity in the sense that validity would be extremely difficult to determine if the diagnostic category was unreliable. Structural Features: Categories Versus Dimensions There are many different ways in which classifications can be constructed. The fundamental choice is between a categorical and a dimensional structure, and it is worth recalling the observation by the philosopher Carl Hempel 40 years ago that, although most sciences start with a categorical classification of their subject matter, they often replace this with dimensions as more accurate measurement becomes possible [40]. The requirement that the categories of a typology should be mutually exclusive and jointly exhaustive has never been fully met by any psychiatric classification, or, for that matter, by any medical classification. Medical, including psychiatric, classifications are eclectic in the sense that they are organized according to several different, coexisting classes of criteria e.g. causes, presenting symptoms or traits, age at onset, course), without a clear hierarchical arrangement. One or the other among them may gain prominence as knowledge progresses or contextual e.g. social, legal, service-related)
CRITERIA FOR ASSESSING A CLASSIFICATION IN PSYCHIATRY 15 conditions change. However, despite their apparent logical inconsistency, medical classifications survive and evolve because of their essentially pragmatic nature. Their utility is tested almost daily in therapeutic or preventive decision-making and in clinical prediction and this ensures a natural selection of useful concepts by weeding out impracticable or obsolete ideas. Categorical models or typologies are the traditional, firmly entrenched form of representation for medical diagnoses. As such, they have many practical and conceptual advantages. They are thoroughly familiar, and most knowledge of the causes, presentation, treatment and prognosis of mental disorder was obtained, and is stored, in relation to these categories. They are easy to use under conditions of incomplete clinical information; and they have a capacity to ``restore the unity of the patient's pathology by integrating seemingly diverse elements into a single, coordinated configuration'' [10]. The cardinal disadvantage of the categorical model is its propensity to encourage a ``discrete entity'' view of the nature of psychiatric disorders. If it is firmly understood, though, that diagnostic categories do not necessarily represent discrete entities, but simply constitute a convenient way of organizing information, there should be no fundamental objection to their continued useÐprovided that their clinical utility can be demonstrated. Dimensional models, on the other hand, have the major conceptual advantage of introducing explicitly quantitative variation and graded transition between forms of disorder, as well as between ``normality'' and pathology. They therefore do away with the Procrustean need to distort the symptoms of individual patients to match a preconceived stereotype. This is important not only in areas of classification where the units of observation are traits e.g. in the description of personality and personality disorders) but also for classifying patients who fulfil the criteria for two or more categories of disorder simultaneously, or who straddle the boundary between two adjacent syndromes. There are clear advantages, too, for the diagnosis of ``sub-threshold'' conditions such as minor degrees of mood disorder and the non-specific ``complaints'' which constitute the bulk of the mental ill-health seen in primary care settings. Whether psychotic disorders can be better described dimensionally or categorically remains an open, researchable question [41]. The difficulties with dimensional models of psychopathology stem from their novelty; lack of agreement on the number and nature of the dimensions required to account adequately for clinically relevant variation; the absence of an established, empirically grounded metric for evaluating severity or change; and, perhaps most importantly, the complexity and cumbersomeness of dimensional models in everyday clinical practice. These considerations seem to preclude, at least for the time being, a radical restructuring of psychiatric classification from a predominantly categorical
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282 INDEX AsociacioÂn PsiquiaÂtri
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294 INDEX US Navy classification 49
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Psychiatric Diagnosis and Classification - ResearchGate

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