A historical approach is helpful in trying to understand how and why the many instruments now available have developed. Hamilton's Rating Scale for Depression, published in 1959, is a good example of the first generation of instruments, most of which are comparatively short and simple. (54) Its contents can easily be printed on one page, and comprise the following:
1. the names of the symptoms to be rated;
2. a rating scale, the same for all the symptoms, by which the presence or absence and the severity of each symptom is recorded;
3. a box in which the rating of each symptom is placed.
No special recommendations about length and style of interview are given, and no explanations or definitions of the symptoms are is given other than what is provided on the rating sheet itself. In other words, the interpretation of the ratings is based on the assumption that the raters have sufficient experience and training to know what most of their contemporaries also mean by the named symptoms. Data analysis is left to the user, other than recommendations about the likely meaning of the sum of the ratings with respect to severity of illness and 'caseness'. This and other early instruments were not tied to the use of any particular set of diagnostic categories, probably because the diagnostic classifications that were available in the 1950s and 1960s were not widely used.
The first generation of instruments made it much easier for researchers to communicate the detailed results of their clinical studies to others, mainly by facilitating the study of changes in symptoms over comparatively short periods of time. The need for this was no doubt connected with the increasing numbers of psychotropic medicines that became available around that time. Measurement of change in symptoms is more immediately useful for the study of response to treatment than reliance upon statements about overall improvement or waiting for a change in diagnosis. But in the absence of guidance about how the symptoms are defined, problems still remain in the interpretation of the results.
Improvements in more recent instruments leading to better quality and meaning of the data they collect have been of two main types, in that the structure and the associated procedures of the instruments have become more elaborate as time has passed. First, the input has been improved by the provision of written descriptions and definitions of symptoms, and by recommending particular styles of interviewing. This implies that researchers using the instrument should carry out preliminary training work so that satisfactory levels of inter-rater reliability are achieved before starting the main study (some examples of the most widely used instruments of this type are described in the next section). Second, the output has been improved by the use of computers to organize and summarize the symptom ratings, allied with the development of widely used psychiatric classifications.
Computer programs based upon decision trees (algorithms) first appeared in the 1970s, and are now commonplace. They allow the specification of sets of symptoms that identify disorders or indicate diagnoses, so that the resulting statements about symptom profiles or the presence of disorders or diagnoses are free from errors of human judgement such as carelessness, simple forgetting, and personal variations from one occasion to the next. But the biases and assumptions built into the programs by their authors still remain, and these may be a problem to others with different opinions.
Programs can also be written to assign disorders and diagnoses according to a selected classification, such as ICD-10 or DSM-IV, and some of the most recently developed instruments such as Schedules for Clinical Assessment in Neuropsychiatry and the Comprehensive International Diagnostic Interview are of this type. When used as intended, the data output from these more recent structured instruments is versatile and of high reliability, but to obtain these benefits the researcher has to pay the penalty of working hard to achieve and to maintain inter-rater reliability.
There are, of course, still plenty of uses for the simpler types of instruments; it is up to those designing and carrying out a study to decide what type of information they need and why, and to select their instruments accordingly. For the sake of those who will be interested in trying to interpret the results, a justification of the quality of the information obtained should always be included in the description of the findings.
Once an instrument (or often a related group of instruments) has demonstrated its usefulness it is likely to stay in use for many years, while at the same time being subject to extensions and improvements. Families of instruments and traditions of interviewing style therefore develop and persist in the major research centres and groups, and it is possible to identify some of these and follow them over the years.
Three such traditions of instrument development are selected for mention so as to illustrate the continuity and close relationships that sometimes exist between different instruments; these relationships may not be apparent from reports of studies in which they have been used. Three research centres that have produced particularly prominent sets of instruments are the Medical Research Council Social Psychiatry Unit at the Institute of Psychiatry in London, Biometrics Research at the New York State Psychiatric Institute at Columbia University, New York, and the Department of Psychiatry at Washington University, St Louis, Missouri. The instruments mentioned below are only a small proportion of the many in the literature, but they are well known because of their association with some large collaborative international research studies and with widely used classifications of psychiatric disorders such as ICD-8, ICD-9, and ICD-10, and DSM-III, DSM-IIIR, and DSM-IV.
At approximately the same time in the early 1960s, but independently, research groups headed by John Wing, at the Institute of Psychiatry of the University of London (at the Maudsley Hospital), and by Robert Spitzer, at the Biometrics Research Unit at the New York State Psychiatric Institute at Columbia University, began to produce structured interviewing and rating schedules that provided extensive coverage of symptoms and were accompanied by recommendations for training procedures.
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