It is important to distinguish between validity and utility in considering psychiatric diagnoses. Diagnostic categories defined by their syndromes should be regarded as valid only if they have been shown to be discrete entities with natural boundaries that separate them from other disorders. Although most diagnostic concepts have not been shown to be valid in this sense, many possess high utility by virtue of the information about outcome, treatment response, and etiology that they convey. They are therefore invaluable working concepts for clinicians.

Computer linkage of an obstetric register and a psychiatric case register made it possible to investigate the temporal relationship between childbirth and psychiatric contact in a population of 470 000 people over a 12-year period: 54 087 births resulted in 120 psychiatric admissions within 90 days of parturition [corrected]. The 'relative risk' of admission to a psychiatric hospital with a psychotic illness was extremely high in the first 30 days after childbirth, particularly in primiparae, suggesting that metabolic factors are involved in the genesis of puerperal psychoses. However, being unmarried, having a first baby, Caesarian section and perinatal death were all associated with an increased risk of psychiatric admission or contact, or both, suggesting that psychological stresses also contribute to this high psychiatric morbidity. Women with a history of manic depressive illness, manic or depressive, had a much higher risk of psychiatric admission in the puerperium than those with a history of schizophrenia or depressive neuroses, and the majority of puerperal admissions met Research Diagnostic Criteria for manic or depressive disorder. Probably, therefore, puerperal psychoses are manic depressive illnesses and unrelated to schizophrenia.

SynopsisFew psychiatric disorders have yet been adequately validated and it is still an open issue whether there are genuine boundaries between the clinical syndromes recognized in contemporary classifications, or between these syndromes and normality. In the long run validation depends on the elucidation of aetiological processes. There are, however, a number of strategies which clinicians could use, but at present rarely do, in order to improve and validate existing classifications. Most of these involve studying populations which have been deliberately chosen to represent a broader grouping than a single diagnostic category, or even a group of related categories.

A representative sample of 105 women were assessed by Goldberg's Standardised Psychiatric Interview (SPI) on two occasions during pregnancy and twice more in the puerperium. Total SPI scores increased significantly after childbirth. Thirteen of the sample had a severe postnatal depression and a further 17 women had milder depression, which in 15 lasted at four weeks. Marked deterioration of their martial relationships was reported by the depressed women but no other social or obstetric characteristics of postnatal depression were found. Women with severe postnatal blues were particularly at risk of developing persistent depressive symptoms subsequently. The only two women referred to a psychiatrist had personality disorders rather than depressive illnesses.

It has often been suggested in recent years that there is no such thing as mental illness; that the conditions psychiatrists spend their time trying to treat ought not, properly speaking, to be regarded as illness at all, or even to be the concern of physicians. Szasz is the best-known exponent of this viewpoint, and the core of his argument is essentially this: that as prolonged search has never demonstrated any consistent physical abnormality in those regarded as mentally ill, and as their ‘illness' consists simply in behaving in ways that alarm or affront other people, or in believing things which other people do not believe, there is no justification for labelling them as ill, and to do so is to use the word illness in a purely metaphorical sense (Szasz, 1960). Schneider had previously been led by the same reasoning to the conclusion that neurotic illness and personality disorders were ‘abnormal varieties of sane mental life’ rather than disease, but he took care to exempt schizophrenia and cyclothymia by assuming that both would in time prove to possess an organic basis (Schneider, 1950). The argument Eysenck puts forward in the first edition of his textbook, though written from the quite different standpoint of academic psychology, is a similar one. After observing that ‘the term psychiatry does not denote any meaningful grouping of problems or subjects of study’ he went on to suggest that the traditional subject-matter of psychiatry should be divided into a small medical part ‘dealing with the effects of tumours, lesions, infections and other physical conditions' and a much larger behavioural part ‘dealing with disorders of behaviour acquired through the ordinary processes of learning’, thereby implying that most of what doctors regarded as mental illness was really learnt behaviour rather than disease, and therefore much better understood, and dealt with, by psychologists than by physicians (Eysenck, 1960). A third line of attack is provided by R. D. Laing, and a fourth is exemplified by the sociologist Scheff. Laing argues that schizophrenia, far from being a disease or a form of insanity, is really the only sane or rational way adolescents have of coping with the intolerable emotional pressures placed on them by society and their families (Laing, 1967). Scheff has developed the somewhat similar argument that what psychiatrists call mental illness is largely a response to the shock of being labelled and treated as insane and the expectations this produces; in other words that schizophrenia is created by the people and institutions that purport to treat it (Scheff, 1963).

The raised incidence of obstetric complications often reported in people with schizophrenia is genuine and probably contributes to the aetiology of the condition.

During the last fifty years, and particularly the last twenty, innumerable different classifications of depressive illness have been proposed, and several disputes are smouldering away between the protagonists of rival schools. Much of this is too well known to need, or bear, repetition. But the conflicting claims and proposals are now so numerous, and methodological problems loom so large, that those who are not intimately involved have increasing difficulty in understanding what is going on; while those who are involved are mostly too intent on developing and promoting their own particular schema to review the overall situation in any broader context. This article is an attempt to describe the main elements in a confusing situation, to outline the important problems, and to indicate the areas of agreement that are beginning to emerge, without advocating any particular solution.

The epidemiological evidence that the offspring of women exposed to influenza in pregnancy are at increased risk of schizophrenia is conflicting. In an attempt to clarify the issue we explored the relationship between the monthly incidence of influenza (and measles) in the general population and the distribution of birth dates of three large series of schizophrenia patients--16,960 Scottish patients born in 1932-60; 22,021 English patients born in 1921-60; and 18,723 Danish patients born in 1911-65. Exposure to the 1957 epidemic of A2 influenza in midpregnancy was associated with an increased incidence of schizophrenia, at least in females, in all three data sets. We also confirmed the previous report of a statistically significant long-term relationship between patients' birth dates and outbreaks of influenza in the English series, with time lags of -2 and -3 months (the sixth and seventh months of pregnancy). Despite several other negative studies by ourselves and others we conclude that these relationships are probably both genuine and causal; and that maternal influenza during the middle third of intrauterine development, or something closely associated with it, is implicated in the aetiology of some cases of schizophrenia.