Disability is a broad concept, covering impairments, activity limitations, and participation restrictions. Impairment is a problem in body function or structure; an activity limitation is a difficulty encountered by an individual in executing a task or action; while a participation restriction is a problem experienced by an individual in involvement in life situations. It is a complex phenomenon, reflecting the interaction between features of a person’s body and features of the society in which they live. Overcoming the difficulties faced by people with disabilities requires interventions to remove environmental and social barriers.
The measurement of disability often differs within and across countries. Among the surveys and censuses used to provide population estimates, questions may differ in terms of wording of instructions and response categories on questionnaires. Some surveys be restricted to assessing physical disabilities such as difficulties related to mobility, sight and hearing, while others may include intellectual impairments or mental health issues. Moreover, measures of disability (and associated response rates) may differ across countries due to varying cultural interpretations of disability. Concerns over differing cultural interpretations can be reduced through assessing difficulties in completing specific activities or functions, rather than direct reference to particular disabilities.
Practitioners recognise question sets by the Washington Group on Disability Statistics as the best instruments for disaggregating the Sustainable Development Goals. These have been developed to increase comparability and better capture functional difficulties respondents face in day-to-day life, and are currently employed across a number of international surveys and censuses.
The Washington Group Short Set on Functioning (WG-SS) identifies persons 5 years of age and over, and covers six core domains of functioning: seeing, hearing, walking, cognition, self-care, and communication. Responses include ‘No difficulty’, ‘Some difficulty’, ‘A lot of difficulty’, and ‘Cannot do at all’ . Disability is classified according to whether a respondent has at least ‘a lot of difficulty’ on at least one of the six questions.
For countries wanting to collect more in-depth information on functional difficulties, the Washington Group has developed several additional question sets. The Washington Group/UNICEF Child Functioning Module consists of 24 questions and determines functional difficulties in the areas such as vision, hearing, mobility, communication, comprehension, behaviour, relationships and emotions for children aged 5-17, with a further submodule for infants aged 2-4 covering concepts such as dexterity and playing.
The enhanced short set (WG-SS Enhanced) is designed to collect information on adult 18 years and above and includes an additional 6 questions regarding upper body functioning, anxiety and depression. The extended set of 36 questions is also intended for adults, and covers additional domains including pain and fatigue.
Users should note that although surveys and census may draw upon Washington group questions, they may not do so exclusively. Incorporation of additional questions, exclusion of key questions, use of dichotomous responses, or employment of different cut-offs in determining disability status will impact comparability. Where possible, the UIS informs users when disability disaggregated estimates are based on Washington Group measures or otherwise.
World Health Organization (WHO)
Washington Group on Disability Statistics (https://www.washingtongroup-disability.com/)