published_or_final_version / abstract / Community Medicine / Master / Master of Public Health

The primary objective of this research was to explore the impact of possible social factors on non-institutionalized adults 18 years of age or older residing in the United States who exhibited severe mental illness (SMI). A holistic sociological model was developed to explain SMI by incorporating elements of social learning theory, social disorganization theory, and gender socialization theory with social demographic factors. Based on the holistic sociological model, the following factors were investigated: demographic aspects of age, education, income and gender; gender socialization; influence of neighborhood area; social network influence based on communication and interaction among peers and family members; and socially deviant behaviors such as frequently smoking cigarettes, drinking alcohol and using drugs specifically marijuana. The impact of these factors on SMI was examined. A sample of 206 respondents drawn from National Survey on Drug Use and Health, 2003 was assessed. These respondents had answered all the questions related to SMI; social deviant behaviors; neighborhood environment; and communications among peers, family members and friends; and the other studied factors. Ordinary linear regression with interaction terms was employed as a statistical tool to assess the impact of social determinants on SMI. Being female, living a disorganized neighborhood, and frequent and high levels of smoking cigarettes and drinking alcohol had a significant influence on SMI. This reevaluation and reexamination of the role of gender socialization path, socially deviant behaviors like smoking and drinking, and community construction on SMI provided additional insights. This research is one of the first to develop a more holistic sociological model on SMI and explored the previously untested interactive relationships. The limitations of this study suggest the need to test a potential recursive research model and explore additional bi-directional associations.

(Truncated abstract) The aims of this thesis are: (i) To estimate the prevalence of psychiatric illness among persons with intellectual disability and, conversely, the prevalence of intellectual disability among persons with a psychiatric illness; (ii) To describe the disability and service utilisation profile of persons with conjoint disorder; (iii) To examine, in particular, intellectual disability co-occurring with schizophrenia; and (iv) To explore the role of hereditary and environmental (specifically obstetric) risk factors in the aetiology of (i) intellectual disability and (ii) intellectual disability co-occurring with psychiatric illness. This thesis has a special interest in the relationship between intellectual disability and schizophrenia. Where data and sample sizes permit, it explores that relationship at some depth and has included sections on the putative nature of the link between intellectual disability and schizophrenia in the introductory and discussion chapters. To realise its objectives, the thesis comprises a core study focusing on aims (i) – (iii) and a supplementary study whose focus is aim (iv). It also draws on work from an ancillary study completed prior to the period of candidacy...This thesis found that, overall, 31.7% of persons with an intellectual disability had a psychiatric illness; 1.8% of persons with a psychiatric illness had an intellectual disability. The rate of schizophrenia, but not bipolar disorder or unipolar major depression, was greatly increased among cases of conjoint disorder: depending on birth cohort, 3.7-5.2% of individuals with intellectual disability had co-occurring schizophrenia. Down syndrome was much less prevalent among conjoint disorder cases despite being the most predominant cause of intellectual disability while pervasive developmental disorder was over-represented. Persons with conjoint disorder had a more severe clinical profile including higher mortality rates than those with a single disability. The supplementary study confirmed the findings in the core body of work with respect to the extent of conjoint disorder, its severity, and its relationship with pervasive development disorder and Down syndrome. Moreover, the supplementary study and the ancillary influenza study indicated a role for neurodevelopmental insults including obstetric complications in the adverse neuropsychiatric outcomes, with timing of the insult a potentially critical element in defining the specific outcome. The supplementary study also added new information on familiality in intellectual disability. It found that, in addition to parental intellectual disability status and exposure to labour and delivery complications at birth, parental psychiatric status was an independent predictor of intellectual disability in offspring as well as a predictor of conjoint disorder. In conclusion, the facility to collect and integrate records held by separate State administrative health jurisdictions, and to analyse them within the one database has had a marked impact on the capacity for this thesis to estimate the prevalence of conjoint disorder among intellectually disabled and psychiatric populations, and to understand more about its clinical manifestations and aetiological underpinnings.