It has been known for a long time that clinical training is sufficiently varied that colleagues of the same discipline, working in the same establishment, are often unable to agree about an individual’s diagnosis, even when presented with exactly the same information 1,2,3,4. An apparent difference in rates of schizophrenia between New York and London proved to be almost entirely due to differences in diagnostic criteria applied to observed phenomenology (5). Observations such as these motivated the development of the formalized sets of diagnostic criteria familiar to us today from the DSM-IV and ICD-10.

The literature on medical decision-making had already shown that clinicians suffer from a number of information
collection biases: 1) They tend to come to diagnostic determinations before they have collected all the relevant information, 2) they tend then to focus on collecting information to confirm that diagnosis (confirmatory bias), 3) they tend to ignore disconfirmatory information, 4) they combine information in idiosyncratic ways, and 5) they tend to make judgments based on the most readily available cognitive patterns (the availability heuristic). Further problems arise because of a tendency to see correlations where none exist (illusory correlation), and to miss real correlations (6).

Added to all these problems is the fact that, even today, standard diagnostic manuals do not provide very detailed descriptions of how to assess psychopathology at the symptom level. All of the criteria for oppositional defiant disorder, for instance, begin with the word “often.” But “how often is often?” There is a great deal of room for clinicians to adopt very different decision rules about when to regard such symptoms as being present.

In the face of all these difficulties it became apparent that methods were required to standardize the collection, quantification, and combination of diagnostic information. As a result, all structured interviews aim to:

In the early days of structured interviews, it was supposed that clinicians would be using them, because it was felt that only they had the necessary training and experience to be able to decide about the presence or absence of symptoms, even when quite detailed definitions were provided. The interview schedule served as a tool to guide the clinician interviewer in determining whether symptoms were present, but the interviewer made the decisions, on the basis of information provided by the child or adult. Interviews of this sort, like the Present State Examination (7) and the Reynard (8) for adults, and the Isle of Wight interview for children 9,10, were the first to be developed, since they sprang naturally from clinical practice. They were called semi-structured because the interviewer was allowed latitude in the specific form of the questions used.