Instruments for the assessment of mental state and behaviour

The instruments now available can be grouped according to the main purposes for which they were designed.

Screening instruments such as the General Health Questionnaire (51> are needed for the identification of likely cases or high risk individuals amongst large populations. These tend to be short and economical in use, since they have to be administered to large numbers of subjects. They are designed to generate a simple score that indicates the status of the subject in relation to the populations upon which the instrument was developed and validated. This is essential for screening and for epidemiological studies, but this single score does not convey much about the details of the subject's feelings or behaviour, and so is of limited interest to the clinician.

Screening instruments are often questionnaires, defining this to mean that they are simply a means of recording the answers to a set of questions, without any further questions or enquiry about the extent to which the subject understands the question or wishes to qualify answers given. Questionnaires are usually filled in by the subject as a 'paper-and-pencil' exercise, as in the General Health Questionnaire, but one widely used questionnaire that has a very detailed content (the Composite International Diagnostic Interview(5,53)) is completed by an interviewer.

Detailed instruments may contain the following.

1. Symptoms of only one type, as in Hamilton's rating scale for depression,(54) or the Scale for Assessment of Negative Symptoms.(55)

2. A selection of symptoms for the study of the relationships between two closely related types, such as depressive and schizophrenic symptoms in the Schedule for Affective Disorders and Schizophrenia. (56>

3. A limited number of items covering different symptoms and behaviour selected as being of special importance, as in the recently developed Health of the Nation Scales of the United Kingdom.(57)

4. A more or less comprehensive array of symptoms that allows the study of the relative distribution of symptoms of many different types, such as Schedules for Clinical Assessment in Neuropsychiatry (58) and the Composite International Diagnostic Interview. (52) Other widely used but less tightly structured instruments with a comprehensive content are the Brief Psychiatric Rating Scaled9.) and the Composite Psychopathological Rating Scale,(60,) aimed at measuring change.

The source and method for collection of information is usually specified by the designers of an instrument. These can include interviews with patients, relatives, and carers, observation of the patient, extracts from other documents, and any combination of these.

The more detailed instruments usually depend upon an interview, and the style of interviewing recommended and the training needed to achieve this depend upon both the quality of the information required and the type of research interviewer for whom the instrument is designed. These vary widely; for instance, Schedules for Clinical Assessment in Neuropsychiatry require a clinical professional training plus a special course for the instrument itself; the Comprehensive Psychopathological Rating Scale, the Brief Psychiatric Rating Scale, and the Structured Clinical Interview for DSM (61> assume a clinical professional training only. The Composite International Diagnostic Interview requires experience in interviewing such as market research plus a special course for the instrument itself, but no clinical professional training.

The time period covered varies from a cross-sectional picture of the present mental state and behaviour ('present' usually being taken to mean the immediately recent period of 2 or 4 weeks), to longer periods of follow-up, personal history, and development, and lifetime histories of psychiatric disorders. The more complicated and lengthy instruments that cover these longer periods are usually designed for particular studies, so are rarely suitable for general use.

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