The concept of need and the development of methods for measuring population needs represent, in a way, a new paradigm in evaluative research and planning of mental health services.
As with all new paradigms, this one has arisen as a way of overcoming a conceptual crisis: the crisis that has resulted from the application of the curative and medical model to the organisation and evaluation of mental health care, and from the traditional way of planning mental health services according to factors more centred on services and staff problems than on the actual problems of the populations.
As is the case with all new paradigms, the concept of needs also represents a radical change at the epistemological level. In fact, this concept integrates a new perspective on: 1. The nature and range of the problems experienced by the mentally ill (seen not only in terms of symptoms and behavioural problems but also in terms of social disability problems); 2. The interventions required to reduce or contain those problems(integrating the dimension of treatment in a more comprehensive dimension of care); 3. The principles of mental health services organisation (seen from a more community-centred perspective).