Primary care as the middle ground for psychiatric epidemiology

The application of epidemiological methods to the study of mental disorder is well established (Dohrenwend & Dohrenwend, 1982). The early focus of attention was understandably directed at institutional populations, where the statistics of time, place and person could be readily collected. Before long it became apparent that these data suffered from contamination by the many nosocomial factors bearing on admission to hospital (Norris, 1959). Latterly there has been a shift of interest to extra-mural studies, many of which are directed at attempts to identify psychiatric illness in the general population. While demographic information may render such samples more representative, these investigations have still to overcome the awkward problems posed by the definition of morbidity. Moreover, despite the development of many sophisticated techniques designed to measure psychopathology, much of the resulting material bears more upon the reliability of the methods used than the validity of the findings (Bartko & Carpenter, 1976). Pari passu, a growing number of enquiries have concentrated on conspicuous psychiatric illness at the level of primary care. The contours of this large segment of morbidity were first delineated in the United Kingdom (Shepherd et al. 1966) and its significance was underlined in 1973 by a World Health Organization European Working Group (World Health Organization, 1973). A recent detailed review of the subject contains close to 600 articles published between 1977 and 1985, most of them originating from Europe and North America, but with a significant minority from the developing world (Wilkinson, 1985). The purpose of the present commentary is to re-assess the current evidence on mental disorder in primary care settings and to outline the rationale for siting the middle ground for epidemiological studies in psychiatry at the level of primary care. The first reason for adopting such a perspective emerges from the findings of health service research on the extent of morbidity vis-a-vis the distribution of patient care (Kalton, 1968). Fig. 1 illustrates the relationship of the mass of morbidity to the three main sources of morbidity statistics in the British National Health Service. Clearly, the bulk of disease comes within the orbit of general practitioner services and major illnesses comprise a relatively small proportion of morbidity. That this is particularly true of psychiatric illness has been demonstrated by a number of studies worldwide which have repeatedly shown that psychiatric illness is among the commoner causes of consultation in general practice. Trends in primary care in the United Kingdom show that diseases of the respiratory system, circulatory system, and mental disorders are the most prominent reasons for consulting general practitioners, accounting for 15-4%, 11-2% and 9-6% respectively of total consultations in 1980 (Balarajan et al. 1983). The figures reported by Shepherd et al. (1966) on the prevalence and distribution of psychiatric illness in general practice yielded a total prevalence rate of 140 per 1000 persons at risk and an inception rate of 52 per 1000 at risk for all types of mental disorder combined. Provisional estimates from the United States indicate that at least 15 % of the US population is affected by mental disorders in one year (Regier et al. 1978), and studies from other countries have yielded comparable findings. Both British and American studies demonstrate that about half of this morbidity is chronic, with a duration of over one year (Shepherd et al. 1966; Regier et al. 1985). However, only a relatively small proportion of the mentally ill who consult general practitioners reach the attention of psychiatrists (Table 1). A second important advantage deriving from the primary care perspective is that it helps resolve the much-vexed definition of a psychiatric 'case' (Wing et al. 1981). For operational purposes this