National Disability Insurance Scheme (NDIS) Population Modelling

Huw Brokensha, Tony Barnes, Andrew Taylor

Research output: Book/ReportCommissioned report - ERA-eligiblepeer-review


As part of the process for introducing the National Disability Insurance Scheme (NDIS) the Productivity Commission (PC) developed a statistical definition, referred to as ‘PC Tier 3’ categorisation, for determining the number of people who might be eligible for services under the NDIS. The PC derived national estimates of the ‘PC Tier 3’ disability population using data from the 2009 Survey of Disability and Carers (SDAC). Later, the Australian Government Actuary (AGA) developed State and Territory estimates from the PC’s SDAC-based ‘PC Tier 3’ national estimate. These jurisdictional estimates were used to derive a ‘target sign-up number’ for regional NDIS trials conducted around the country.

The Northern Territory Department of Health’s experience with the sign-up phase of the NT Barkly Region trial led them to question the Territory sign-up targets, and by implication the associate ‘PC Tier 3’ AGA derived NT estimates. As a consequence this research project, which assesses the quality of current NDIS eligible population estimates for the Territory and explores the development of other estimates, was undertaken.

This research demonstrates that the SDAC survey, while being well suited to deriving national ‘PC Tier 3’ population estimates, is demonstrably unsuitable for deriving NT NDIS estimates for reasons of highly restricted scope and coverage and inadequate sample size. The Australian Bureau of Statistics (ABS) openly acknowledged the limitations of SDAC in the Territory. As a consequence, the AGA derived Territory estimates must be viewed as unsound and unreliable.

We explored and assessed other available data sources (sometimes as combinations of two data sources) for their suitability for deriving satisfactory estimates of the NT disability population. Two sets of data, each a combination of two other ABS datasets, were found to be suitable for this task. The first combined dataset is constructed from the 2011-12 National Health Survey (NHS) and the 2012-13 National Aboriginal and Torres Strait Islander Health Survey (NATSIHS). Neither of these datasets is fit-for-purpose on its own but suitable estimates can be derived from the two sets together. The second suitable data source is the 2011 Census of Population and Housing (Census) used in conjunction with the ABS derived 2011 Estimated Resident Populations (ERPs).
From each of these two sets of combined datasets, estimates of disabled populations based on the individual dataset’s own measures of disability (‘profound or severe’ core functional limitation in the case of the NHS/NATSIHS, and ‘has need of assistance’ with core functional activities from the Census/ERP) were made. These estimates can be converted to the preferred ‘PC Tier 3’ disability population scale using adjustment ratios derived using SDAC data. Further, estimates of the NDIS eligible population for the Territory can be derived by subtracting estimates of the 50-64 year old Indigenous ‘PC Tier 3’ Territorians who will be Commonwealth supported. The various ABS disability measures, including the NDIS eligible population estimate for the Territory that we have developed, are set out in this report commissioned by the Northern Territory Government.
Original languageEnglish
Place of PublicationDarwin, NT
PublisherCharles Darwin University
Commissioning bodyNT Department of Health
Number of pages99
Publication statusPublished - 2016


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