Many individuals with mental retardation (MR) have mental health disorders that are undiagnosed and untreated (Reiss & Valenti-Hein, 1994). Individuals with MR experience the full range of emotional, psychiatric and behavioral disorders at higher frequencies than the general population (Kishore, Nizamie & Nizamie, 2010; Prout, 1993). Prevalence studies have shown that individuals with MR are three to four times at higher risk for psychopathology than are individuals without MR (Matson & Bamburg, 1998; Prout, 1993). This is known as a dual diagnosis, which describes the finding of MR in association with significant psychopathology (Prout, 1993). While, psychopathology is limited to those phenomena and disorders that are described in the conventional classification systems such as the Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV). Examples include anxiety, depression, paranoia, dependent personality traits, avoidant behaviour and thought disorder (Reiss & Valenti-Hein, 1994).
These disorders are distressing to the individuals who experience them and they have a variety of detrimental side effects on the individual and on others. These behavioural and mental health problems are barriers for successful community placement and integration; they increase support needs; they are associated with physical restraints and pharmacological interventions; they impact family by causing stress and by imposing financial sacrifices and can weigh on staff time, energy and morale (Rojahn, Rowe, Kasdan, Moore & van Ingen, 2011).
However, identifying and diagnosing individuals with MR and other mental health disorders is a complicated process. Traditional methods of diagnosis rely on direct communication with patients (Kishore et. al, 2010). Nonetheless, individuals with MR exhibit communication and cognitive difficulties making it difficult for them to report psychiatric problems (Kishore et. al, 2010; Matson & Bamburg, 1998). Furthermore, although there are various psychological tools available for psychiatric evaluation in general, their validity with MR is questionable (Kishore et. al, 2010). For example, many of them were standardized on populations without MR and/or their mode of assessment, item content and norms may be inappropriate (Kishore et. al, 2010; Prout, 1993). In order to accurately assess and diagnosis psychopathology in individuals with MR, researchers have developed new scales to assess psychopathology in individuals with mild or moderate MR (Matson & Bamburg, 1998).
In developing the criteria for a dual diagnosis instrument, researchers have noted three characteristics of psychopathology. The first is that the same core content is included in all widely used psychopathology classification systems, such as anxiety, depression paranoia, etc. Second, mental disorders are indicated by patterns of symptoms, rather than by a single one. Lastly, the onset of mental disorders is indicated by a significant deterioration...