A study of behaviour problems and psychiatric disorders among people with intellectual disability

The present thesis investigates behaviour problems and their relationship to psychiatric disorders in people with intellectual disability living in the northern part of Norway, as well as the concordances between four of the most commonly used assessment instruments for psychiatric disorders in people with intellectual disability. A total of one hundred and eighty-one individuals with intellectual disability living in the counties of Nordland, Troms and Finnmark participated in the studies. Four checklists for psychiatric disorders in people with intellectual disability were used: the Reiss Screen, the Mini Psychiatric Assessment Schedule for Adults with Developmental Disability, Mini PAS-ADD, the Diagnostic Assessment for the Severely Handicapped–II, DASH-II, and the Assessment of Dual Diagnosis, ADD. The Aberrant Behavior Checklist was used to assess behaviour problems, Vineland Adaptive Behavior Scales was used to measure adaptive functioning and Leiter International Performance Scale, Wechsler Intelligence Scale for Children-Revised-III or Wechsler Adult Intelligence Scale-III were used to assess cognitive functioning. A checklist developed for the project was used to assess service needs. Behaviours rated as problems by family and care staff was common in the individuals with administratively defined intellectual disability. Twenty percent of the participants were reported to have severe behaviour problems and this corresponded to a prevalence rate of 63.6 people per 100 000 people in the general population when calculated relative to the corresponding age group in the general population. On the average, people showing challenging behaviour had seven behaviours rated as severe problems. People with severe behaviour problems were less likely to have friends and were perceived to be significantly less satisfied with their life-situation than people without severe behaviour problems. The participants with moderate and severe behaviour problems showed significantly more symptoms of psychiatric disorders than those without such problems, and the majority of the participants with behaviour problems had symptoms of the main psychiatric disorders. The participants with mild and moderate intellectual disability showed more symptoms of psychosis and depression than the participants with severe and profound intellectual disability. There were no direct associations between individual behaviour problems and psychiatric disorders, but the group with mild/moderate intellectual disability showed a somewhat different pattern of associations than the group with severe/profound intellectual disability. Depression was associated with screaming and aggression in the participants with severe and profound intellectual disability, and with self-injury in the participants with mild and moderate intellectual disability. On the four checklists for psychiatric disorders used in the project, the correlations between the participants’ sum scores were moderate to high, suggesting that the checklists give fairly similar indications of the psychiatric health status of the participants. The concordances between individual corresponding scales, however, were lower, suggesting that these scales do not measure the same underlying problems. The results indicate that psychiatric disorders are prevalent among people with behaviour problems. The evaluations of the assessment instruments suggest that the four assessment instruments used in the present project may be useful for identifying such disorders in people with intellectual disability, but the checklists seemed to be most useful as general indicators of psychiatric disorders and of less value for specifying the nature of the disorders