The aim of this chapter is to describe a stepwise approach toward an evidence base for planning or re-forming mental health services. In section 10.1 we describe this pathway in terms of the background epidemiological information which can support service development. In section 10.2 we discuss the different components of a mental health system of care, both with respect to their categories and their capacities. In section 10.3, we discuss how local service utilisation data can contribute to the evidence base that should inform planning decisions.

Although we present in this section an approach to assessing the need for mental health services, these estimates cannot be properly interpreted without first considering overall health and social care needs of the population in question. This is because it is misleading to discuss mental health needs without consideration of wider family and other social networks. Further, the specialist mental health services do not operate alone, but rather function at a whole series of interfaces with other social and health care agencies, all of which are under the influence of the wider social, political and cultural climate.

To illustrate this point, we shall refer to a enquiry carried out by Mueller (1973) in which he contacted 18 leading social psychiatrists in six countries asking for their views on the ideal psychiatric service for a population of 100000. However, reflecting the socio-political climate of the time, Franco Basaglia, in reply, refused to give figures on that basis. He criticized the way the question was put, and underlined the need for extensive background information about each particular area before any estimate of local service needs can be made. His objection would be seen as self-evident now.