ABSTRACT
More than 20 per cent of the general population living in the community have a ‘psychiatric disorder’ of some kind (Jenkins, Lewis, Bebbington, Brugha, Farrell et al., 1997; Kessler, 1995). However, reported prevalence rates for people with intellectual disability differ widely. For example, Sturmey, Reed and Corbett (1991) reported rates that vary between 10 per cent and 39 per cent. Such variation is due to a variety of factors such as sample selection, the type of diagnostic methods (self-report, carers’ reports, observation), and definitions of psychiatric disorder and learning disability used. The usefulness of psychiatric diagnosis has been queried both for the general population (Boyle, 2002) and for people with intellectual disability (Slade and Bentall, 1988). An alternative way of assessing the causative and maintaining factors of psychological distress is to adopt a formulation approach (Persons, Davidson and Tompkins, 2000). Individualized case formulation is at the core of cognitive behavioural therapy (CBT) and consists of an idiographic (individualized) theory that is linked to a nomothetic (general) cognitive behavioural theory (Tarrier, 2006).
