A system dynamics modelling approach to studying the increasing prevalence of people with intellectual developmental disorders in New South Wales

Objective The aims of this study were to estimate the prevalence count of people with intellectual developmental disorders (IDD) in New South Wales (NSW) in 2003, by age groups, and to forecast their prevalence until 2043. Methods Administrative data obtained from NSW government departments of education, pensions, health and disability were used to profile the number of people whose characteristics met the criteria for 'intellectual developmental disorders' who had received services in 2003. These figures were compared with published tables of NSW data from the national self-report Survey of Disability, Ageing and Carers (SDAC) of 2003 to estimate the likely prevalence of people with intellectual developmental disorders, by age groups in that year. The results were then used as baseline figures in a computational system dynamics model of the aging chain of people with these disorders, built to project prevalence to 2043. Results The number of people who met the criteria for having intellectual developmental disorder in NSW in 2003 was estimated to be 57000 (a ratio of 85 per 10000), with 32000 aged 0-15 years, 15000 aged 16-39 years, 9000 aged 40-64 years and 1000 aged 65+ years. Using these figures as baseline, the computer simulation predicted a total increase to 77225 people in 2013 and 135905 people by 2043. By 2043, the number of children with intellectual developmental disorders will have doubled, from 32000 to 59480, and the number of adults will have tripled, from 25000 to 76420. Conclusions This modelling technique forecast an increase in the prevalence count of people with intellectual developmental disorders in NSW over the period 2003-43 from 57000 (85 per 10000) to 135905 (135 per 10000). These predictions may have important implications for the planning of specialist health services for this group of people.