DEFINITION OF SCALES
Saturday, November 14th, 2009A scale consists of a defined continuum or dimension along which judgments are placed. The scale may be a set of ordered categories with numbers attached corresponding increasing or decreasing amount of severity or other quantitative characteristics of the phenomena being observed. The form of a psychological scale is dependent on particular psychometric techniques; the content, however, is dependent on the underlying psychological theory as noted by Hamilton (6). Psychiatric scales are special kinds of psychological scales. They derive their form from the science of psychological scales in general (about which there is a vast literature) and their content from underlying theories and notions concerning the nature of psychiatric illness thought relevant by various schools of psychiatry. Characteristics of Clinical Scales in Affective Disorders For practical purposes clinical scales in psychiatry have been divided by Garside (4) into four main types, each with distinct characteristics. The first type is the assessment or descriptive scale that can be used to assess the degree of psychiatric illness such as depression. An example of this type of scale is the Hamilton Depression Scale (HDS) (5). The second is discriminatory rather than descriptive, and may be useful in arriving at a psychiatric diagnosis; an example of this scale is the Newcastle Diagnostic Index (2). The essential feature of a descriptive scale is that individual items should correlate more highly among themselves and give rise to a general factor indicating that it is meaningful to describe patients along such a dimension, i.e., convergent validity. In diagnostic scales, it is essential that the items produce separate correlational groups, i.e., discriminant validity. While there appears to be some general agreement on empirical findings with the use of descriptive scales (12), there has been little general agreement on findings on diagnostic scales in depression, for instance. Descriptive scales have also been referred to as quantitative scales to distinguish them from qualitative ones, e.g., discriminatory or diagnostic scales (1). The other types of scales are predictive, in the sense of predicting the course and outcome of particular psychiatric conditions, as in Kerr et al. (8), Paykel (11), and Carney et al. (2). These latter scales will not be discussed further in any detail. There are a number of commonly used and established descriptive scales for measuring anxiety and depression (Table 1). The main uncertainty in their use centers on the question of validity. There are uncomfortably high correlations between any of the scales listed measuring depression and those designated to measure anxiety (10). For instance, the Hamilton Depression and Hamilton Anxiety Scales show intercorrelations of around 0.5 to 0.6 in the literature. This could suggest that clinical anxiety and depression are highly correlated. However, impure scales could magnify this relationship, and most of our present scales fail to distinguish anxiety from depression adequately enough. What if, for instance, the HDS was not a sufficiently pure measure of the illness termed depression. After all, it was designed on a logical empirical basis by Max Hamilton, although he did go on to examine its psychometric properties. What if the margin of error in accuracy was, say 30% or even 50%, where would that leave interpretations of amine levels or pharmacological treatment indices, when the HDS is the critical variable?
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