Robert E. Kendell THE ROLE OF DIAGNOSIS IN PSYCHIATRY London: Blackwell Scientific Publications, 1975 (distributed by J. 8. Lippincott Company, Philadelphia), 176 pp., $14.
For a variety of reasons, psychiatric diagnosis, which used to be of interest to only a small portion of our profession, has increasingly become a subject of intense interest, debate, and even acrimony. There is hardly a current issue facing our profession that does not affect our diagnostic system, whether it is our role as physicians, the utility of the medical model, new somatic treatments, computerization of health-care data, or third-party payment. This short book by Robert Kendell, Professor of Psychiatry at the University of Edinburgh, is absolutely essential reading for anyone interested in examining the role of diagnosis in psychiatry.
Each of the 11 chapters is organized around an important issue in psychiatric diagnosis. The only issue in the American contemporary scene regarding diagnosis that is not discussed is third-party payment. This is not surprising, since the British method of health-care financing does not require the physician to indicate treatment for a "legitimate" medical diagnosis before payment is given for services rendered.
In the first chapter, "The Importance of Diagnosis," Kendell reviews the arguments against diagnosis in psychiatry and clearly demonstrates that, despite the shortcomings of psychiatric diagnosis and the possibilities for misuse, our profession cannot function without some form of classification system. Chapter 2, "The Nature of Disease and Diagnosis," reviews various concepts of medical disease to demonstrate that our difficulty in defining psychiatric disorders is fundamentally no different from a persistent difficulty in defining the more general rubric of medical disease. Chapter 3, "Issues of Reliability and Validity," reviews studies of the reliability of psychiatric diagnosis, various statistical indices for measuring diagnostic agreement, and various criteria that can be used for establishing the validity of diagnostic categories. Chapter 4, "Diagnosis as a Practical Decision -Making Process," provides evidence that most diagnostic decisions are made early in the course of a diagnostic interview and are largely dependent upon what the patient says, rather than observations made of overt behavior.
Chapter 5, "Disease Entities in Psychiatry," clarifies the meaning of the concept of "disease entity" in medicine and in psychiatry. Using the criterion of discontinuity, Kendell argues that there is little, if any, convincing evidence supporting the disease-entity status of functional psychiatric diagnoses. However, he also indicates that there are clearly established medical disorders, such as essential hypertension, that do not have sharp boundaries justifying status as disease entities. Chapter 6, "International Differences in Diagnostic Criteria," reviews the wellknown studies indicating large and important differences in diagnostic usage in different countries. Dr. Kendell was one of the principal investigators in the U.S./U.K. Diagnostic Project, which studied differences in diagnostic practice in this country and Britain. That diagnostic differences between our two countries are not limited to psychiatry is heartening. Apparently what is known as chronic bronchitis in London is diagnosed as emphysema in Chicago. Chapter 7, "International Classification," reviews the various attempts to provide an international classification of mental disorders, from earliest times up to and including the ninth edition of the International Classification of Diseases. Chapter 8, "The Role of Multivariate Analysis in Deriving or Validating Classifications," presents various statistical approaches to developing and validating diagnostic categories. This chapter will be tough going unless the reader has a considerable degree of statistical sophistication.
Chapter 9, "The Choice Between Categories and Dimensions," presents the arguments for each of these approaches to classifying psychiatric phenomena. Kendell concludes that despite the theoretical advantages of dimensional representation of functional psychiatric phenomena, clinicians will continue, for practical purposes, to use categories (diagnoses). Chapter 10, "Defining Diagnostic Criteria," reviews attempts at improving the reliability of psychiatric diagnosis by providing glossaries of definitions, operational criteria, and computer analysis of psychiatric symptoms. Kendell points out the central issue of definition - that is, indicating which features of the category are essential and always present, which features are commonly present but may be absent, and, finally, which features must be absent for the diagnosis to be made.
As our own profession begins to examine the third edition of the American Psychiatric Association Diagnostic and Statistical Manual (DSM ??), we would be well advised to become familiar with the issues discussed in this book. I wish I had written it.