Three major classes of purposes were selected for identifying persons with disabilities at the aggregate level:
- to provide services, including the development of programs and polices for service provision and the evaluation of these programs and services
- to monitor the level of functioning in the population
- to assess equalization of opportunities
The intent of these purposes for measurement is consistent with that of the Sustainable Development Goals, which outlines major goals for policy formulation and program planning, internationally. The common goal is to promote the participation of persons with disabilities in all aspects of life.
The full 2004 Washington Group Proposed Purpose of an Internationally Comparable General Disability Measure provides an in-depth explanation of the development of the WG purposes and methodology.
There is also a chapter on the purpose of disability measurement in a forthcoming book on the work of the WG – Altman, B., Rasch, E. (2016) Purpose of an International Comparable Census Disability Measure. In B. Altman (Ed), International Measurement of Disability: Purpose, Method and Application. Springer: Social Indicators Research Series 61.
The work plan for the development of the Extended Question Set on Functioning known as The Matrix provides an overview of the types of information on disability that can be collected. It also records the status of which items the WG already has tools for, which are under development, and which the WG are not working on at this time.
Many purposes exist for collecting disability data. Depending on the purpose, information may need to be collected at the body function and structure, activity, or participation level (see The World Health Organisation’s International Classification of Functioning, Disability and Health). Furthermore, depending on space constraints on data tools or the purpose of data collection, a wider or narrower range of functional domains should be considered. Sometimes functioning needs to be measured taking into account the use of assistive devices (wheelchairs, canes, etc.) or personal assistance, and sometimes without, depending on the reason for collecting data. Similarly, sometimes information on the cause of disability or age of onset of disability (or other factors) is important.