Abstract:
Only in the last 10 years have researchers and clinicians begun to acknowledge the significance of mental health issues for people with intellectual disabilities (IDs). Initial research has focused on identifying rates of mental health disorder (MHD, i.e. mental, personality, and behavioural disorders) in this population. While figures are available regarding the prevalence of MHDs from overseas studies, no research has been undertaken using New Zealand samples. The aim of the first part of this thesis is to establish the prevalence of MHD in a sample of adult New Zealanders with IDs. Seventy three clients from a local community agency were screened for the presence of MHDs using two assessment instruments - the Reiss Screen for Maladaptive Behaviour (Reiss Screen), and the Psychopathology Instrument for Mentally Retarded Adults (PIMRA). Results indicated that the overall rate of MHD in the sample was around one in three (31.8 - 33.3%). This figure is comparable with those reported overseas. Consistent with overseas research it is considerably greater than rates recorded for the general population. The implications of this high prevalence are discussed in terms of the importance of thorough screening for mental health difficulties in those with an ID. The prevalence of individual disorders was also assessed. Consistent with overseas findings high rates of personality and behavioural disturbance contributed to the high overall rates of MHD in the sample. However, a lack of evidence for the validity of the PIMRA and the Reiss Screen as diagnostic instruments indicates that the reported rates of individual disorders be viewed only as preliminary estimates.
The second part of the thesis addressed the lack of research on theories of psychopathology in ID. Traditionally theories developed for the general population have been assumed to generalise to individuals with an ID, without being validated for that group. The second study in the thesis aimed to assess the applicability to people with an ID of findings regarding information processing in anxiety for the general population. The particular characteristic investigated was attentional bias towards threat. Groups of 8 high- and 8 low-trait anxious individuals with mild IDs participated in a replication of MacLeod, Matthews, and Tata's (1986) study using the visual probe paradigm. The attentional bias toward threatening stimuli found in the general population was not observed in the present investigation. While it is possible that attentional bias towards threat is not an aspect of information processing in anxiety when concurrent with ID, it is suggested that the stimuli used in the present study were not perceived as threatening enough to elicit an effect. Differences in information processing between high- and low-trait anxious participants were indicated however, with high-trait anxious individuals displaying significantly shorter detection latencies for both threatening and non-threatening stimuli. This result is discussed in terms of a possible task sensitivity and general hypervigilance in anxious individuals with IDs. Implications regarding the treatment of anxiety in this group are also considered.
